GRE tunnel limitations

Please i want to know if the GRE tunnel has limitation for traffic passes over it depend only on physical media.
Example:if i want 5GIG traffic to pass over GRE tunnel and physical media have BW 10 GIG ,GRE tunnel can handle this amount of traffic or not.

it's depends on you equipment. if you have something like asr1000 on both sides (or other device which handle gre in hardware), you can achieve speed more than 5gbps.

Similar Messages

GRE tunnel feature limitation on Cisco Catalyst 4500X

Hi,
I have a customer with three sites. They have the Cisco catalyst 4500-X at each sites and wish to create GRE tunnels between each of these switches.
I have a vague reference which tells me the Cisco cat 4500-x or any cat 4500 for that matter does have severe limitations when GRE tunnels are created, especially limiting the bandwidth to 70kbps. Its also not recommended for data traffic but control plane traffic.
Please advice.

No experts to answer this?

GRE tunnel default MTU

Anybody know the default mtu setting on a gre tunnel interface such as this?:
interface Tunnel1
description "xxx"
ip address x.x.x.x 255.255.255.252
tunnel source Loopback1
tunnel destination x.x.x.x
I'm asking cause on the core redundant to this one where I've copied code from, the config line 'ip mtu 1500' is configured. I want to make sure these are matched up.
Thanks in advance.
/rls

Robert,
Sorry, I spoke too soon. I should have focused on your question, which is "IP MTU" and referred you to the command "show ip interface Tu0" instead of "show interface tu0".
GRE packets are formed by the addition of the original packets and the required GRE
headers. These headers are 24-bytes in length and since these headers are added to the
original frame, depending on the original size of the packet we may run into IP MTU
problems.
Even though the maximum IP datagram has been defined as 64K, most links enforce a smaller
maximum size for the packets. This maximum size is known as MTU (Maximum Transmission
Unit) and as you also know, different types of media have different MTU sizes they can
accommodate and transport. The most common IP MTU is 1500-bytes in length (Ethernet).
The IP implementation, as we know it, provides a mechanism to allow routers the
fragmentation and transmission of packets larger if there are differences in the MTU and a
packet is larger than what the outgoing media will support. Once a packet has been
fragmented to be sent over a media that will not support the original packet size, the end
station is responsible for the reassembly of the different fragments the original packet
was broken into.
GRE tunnels normally calculate their IP MTU size based on the physical link they will use
as the outgoing interface.
What you see in âshow interface Gig Xâ is the MTU of the interface and NOT the IP MTU.
In order for you to see the IP MTU you need to use the âshow ip interface Gig Xâ
When the tunnel is created, it deducts the 24-bytes it needs to encapsulate the passenger
protocols and that is the IP MTU it will use.
For example, if we are forming a tunnel over FastEthernet (IP MTU 1500) the IOS calculates
the IP MTU on the tunnel as:
1500-bytes from Ethernet - 24-bytes for the GRE encapsulation = 1476-Bytes
Let me explain this with a simple set up:
Lets say I configure a Tunnel interface and sourcing it via a physical interface which has an MTU of 1500, then the Tunnel
interface will have IP MTU of 1476, leaving space for the 24 byte GRE Header.
In my case, I am sourcing the packets from Gig0/0 which has physical interface of MTU 1500, so when I do a "show ip int Tu0",
You will see that the IP MTU is 1476.
Router#sh run int gi0/0
Building configuration...
Current configuration : 118 bytes
interface GigabitEthernet0/0
ip address 10.89.245.253 255.255.255.0
duplex auto
speed auto
media-type rj45
end
Router#sh run int tu0
Building configuration...
Current configuration : 127 bytes
interface Tunnel0
ip address 1.1.1.1 255.255.255.252
tunnel source GigabitEthernet0/0
tunnel destination 10.89.245.1
end
Router#sh int gi 0/0
GigabitEthernet0/0 is up, line protocol is up
Internet address is 10.89.245.253/24
MTU 1500 bytes, BW 100000 Kbit, DLY 100 usec,
Router#sh ip int tu 0
Tunnel0 is up, line protocol is up
Internet address is 1.1.1.1/30
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1476 bytes
Now, lets say I lower the IP MTU value on Gi0/0 to 1400, What should be the default new value on the tunnel interface?? You
are absolutely right, 1376 :-)
Router#sh run int gi0/0
Building configuration...
Current configuration : 131 bytes
interface GigabitEthernet0/0
ip address 10.89.245.253 255.255.255.0
ip mtu 1400
duplex auto
speed auto
media-type rj45
end
Router#sh ip int tu0
Tunnel0 is up, line protocol is up
Internet address is 1.1.1.1/30
Broadcast address is 255.255.255.255
Address determined by setup command
MTU is 1376 bytes
Please standby.... More to follow in the second post due to character limitation
Regards,
Arul
** Please rate all helpful posts **

How many numbers of GRE Tunnels are supported on Cisco 3925 router?

Hi...
I would like to know that.......
How many numbers of GRE Tunnels are supported on Cisco 3925 router?
Thanks....

This is what I found in my search:
There may be factors such as memory constraints that will place practical limits on how many tunnels you can support. But there is also a hard limit on the number of tunnels that you can configure. That limit is based on the limitation of the number of IDBs supported by your router. The IDB is the Interface Descriptor Block and each interface (physical, or tunnel, or loopback, or whatever) requires an IDB. The number of IDBs will vary by platform and sometimes by release level of the code that you are running. You can use the privileged command show idb to see what the limitation is on your router. On the 1841 router that I just checked the limit on IDB is 1200 (which is a pretty large number - I believe that you would encounter other limits on performance or on size of configuration before you exhaust the IDB limit).
https://supportforums.cisco.com/thread/2007932
Hope it helps.
Jatin Katyal
- Do rate helpful posts -

GRE tunnel could not be used by the hosts connected to the router

Hi,
I am using cisco ASR1013 (RP2) and a Mikrotik Router for setting up a GRE tunnel for LAN to LAN routing over a broadband link. The tunnel works fine (able to ping tunnel end points and also all the connected interfaces on both the Mikrotik and Cisco ASR) but the hosts that are connected directly to the Cisco router interface over a layer 2 cisco switch are unable to connect (ping) the hosts or connected interfaces on the mikrotik side. I am sure its not a mikrotik issue as i dont see any traffic coming through the tunnel using the mikrotik torch utility. There are no ACL's or firewall rules on any of the devices......
Source and destination of the tunnel are public IP's and are pingable via internet (The tunnel is connected and endpoints are pingable)
Mikrotik connected interface IP = 192.168.253.1/24
Mikrotik tunnel end point IP = 192.168.254.1/30
Cisco tunnel end point IP = 192.168.254.2/30
Connected cisco subnet to reach Mikrotik = M.N.O.32/28
Cisco interface IP for LAN = M.N.O.33
Test host IP on the LAN subnet = M.N.O.34
The below is my Cisco config
ASR-1#sh run int tun 1
Building configuration...
Current configuration : 144 bytes
interface Tunnel1
ip address 192.168.254.2 255.255.255.252
ip mtu 1400
tunnel source A.B.C.D
tunnel destination W.X.Y.Z
end
ASR-1#sh run int g0/1/7
Building configuration...
Current configuration : 280 bytes
interface GigabitEthernet0/1/7
description LAN
ip address M.N.O.33 255.255.255.240
ip verify unicast source reachable-via rx
no negotiation auto
cdp enable
end
ASR-1#sh ip ro 192.168.253.1
Routing entry for 192.168.253.0/24
Known via "static", distance 1, metric 0 (connected)
Routing Descriptor Blocks:
* directly connected, via Tunnel1
Route metric is 0, traffic share count is 1
ASR-1#ping 192.168.253.1 so M.N.O.33
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to 192.168.253.1, timeout is 2 seconds:
Packet sent with a source address of M.N.O.33
Success rate is 100 percent (5/5), round-trip min/avg/max = 5/5/6 ms
ASR-1#pi M.N.O.34
Type escape sequence to abort.
Sending 5, 100-byte ICMP Echos to M.N.O.34, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 1/1/1 ms
If i try to ping 192.168.253.1 (network connected to Mikrotik) from the host M.N.O.34 (the gateway of this host is M.N.O.33 - Int g0/1/7 of the Cisco ASR), i cannot reach detination - request timed out.... Below are the results of trace and ping from the host connected to ASR G1/0/7
PING TO THE GATEWAY *********
[root@localhost ~]# ping M.N.O.33
PING M.N.O.33 (M.N.O.33) 56(84) bytes of data.
64 bytes from M.N.O.33: icmp_seq=1 ttl=255 time=0.161 ms
64 bytes from M.N.O.33: icmp_seq=2 ttl=255 time=0.143 ms
^C
--- M.N.O.33 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1357ms
rtt min/avg/max/mdev = 0.143/0.152/0.161/0.009 ms
PING TO THE TUNNEL END POINT IN CISCO ASR
[root@localhost ~]# ping 192.168.254.2
PING 192.168.254.2 (192.168.254.2) 56(84) bytes of data.
64 bytes from 192.168.254.2: icmp_seq=1 ttl=255 time=0.141 ms
64 bytes from 192.168.254.2: icmp_seq=2 ttl=255 time=0.141 ms
^C
--- 192.168.254.2 ping statistics ---
2 packets transmitted, 2 received, 0% packet loss, time 1739ms
rtt min/avg/max/mdev = 0.141/0.141/0.141/0.000 ms
PING TO THE TUNNEL ENDPOINT IN MIKROTIK
[root@localhost ~]# ping 192.168.254.1
PING 192.168.254.1 (192.168.254.1) 56(84) bytes of data.
^C
--- 192.168.254.1 ping statistics ---
11 packets transmitted, 0 received, 100% packet loss, time 10413ms
PING TO THE CONNECTED INTERFACE ON MIKROTIK
[root@localhost ~]# ping 192.168.253.1
PING 192.168.253.1 (192.168.253.1) 56(84) bytes of data.
^C
--- 192.168.253.1 ping statistics ---
4 packets transmitted, 0 received, 100% packet loss, time 3641ms
TRACE TO THE CONNECTED INTERFACE ON MIKROTIK
[root@localhost ~]# traceroute 192.168.253.1
traceroute to 192.168.253.1 (192.168.253.1), 30 hops max, 60 byte packets
1 M.N.O.33 (M.N.O.33) 0.180 ms 0.156 ms 0.145 ms
2 * * *
3 * * *
4 * * *
5 * * *
Please help

Hi,
Sorry for the delayed response ....Both ends static routes are added for the connected test interfaces.....
Regards,
Mahesh

IP routing utilizing Verizon private network (GRE tunnel) with remote cellular gateways

Okay, I give up, and think I have done my due diligence (I have been engrossed and fascinated spending many more hours than allotted to try and learn some of the finer details). Time for some advice. My usual trade is controls engineering which generally require only basic knowledge of networking principals. However I recently took a job to integrate 100 or so lift stations scattered around a county into a central SCADA system. I decided to use cellular technology to connect these remote sites back to the main SCADA system. Well the infrastructure is now in and it’s time to get these things talking. Basic topology description is as follows: Each remote site has an Airlink LS300 gateway. Attached to the gateway via Ethernet is a system controller that I will be polling via Modbus TCP from the main SCADA system. The Airlinks are provisioned by Verizon utilizing a private network with static IP's. This private networks address is 192.168.1.0/24. Back at the central office the SCADA computer is sitting behind a Cisco 2911. The LAN address of the central office is 192.168.11.0/24. The 2911 is utilizing GRE tunnels that terminate with Verizon. The original turn up was done with another contractor that did a basic config of the router which you will find below. As it stands now I am pretty confident the tunnels are up and working (if I change a local computers subnet to 255.255.0.0 I can surprisingly reach the airlinks in the field), but this is obviously not the right way to solve the problem, not to mention I was unable to successfully poll the end devices on the other side of the Airlinks. I think I understand just about every part of the config below and think it is just missing a few items to be complete. I would greatly appreciate anyone’s help in getting this set up correctly. I also have a few questions about the set up that still don’t make sense to me, you will find them below the config. Thanks in advance.
no aaa new-model
ip cef
ip dhcp excluded-address 10.10.10.1
ip dhcp pool ccp-pool
import all
network 10.10.10.0 255.255.255.248
default-router 10.10.10.1
lease 0 2
ip domain name yourdomain.com
no ipv6 cef
multilink bundle-name authenticated
username cisco privilege 15 one-time secret
redundancy
crypto isakmp policy 1
encr 3des
hash md5
authentication pre-share
group 2
crypto isakmp key AbCdEf01294 address 99.101.15.99
crypto isakmp key AbCdEf01294 address 99.100.14.88
crypto ipsec transform-set VZW_TSET esp-3des esp-md5-hmac
mode transport
crypto map VZW_VPNTUNNEL 1 ipsec-isakmp
description Verizon Wireless Tunnel
set peer 99.101.15.99
set peer 99.100.14.88
set transform-set VZW_TSET
match address VZW_VPN
interface Tunnel1
description GRE Tunnel to Verizon Wireless
ip address 172.16.200.2 255.255.255.252
tunnel source 22.20.19.18
tunnel destination 99.101.15.99
interface Tunnel2
description GRE Tunnel 2 to Verizon Wireless
ip address 172.16.200.6 255.255.255.252
tunnel source 22.20.19.18
tunnel destination 99.100.14.88
interface Embedded-Service-Engine0/0
no ip address
shutdown
interface GigabitEthernet0/0
description $ETH-LAN$$ETH-SW-LAUNCH$$INTF-INFO-GE 0/0$
ip address 10.10.10.1 255.255.255.248
shutdown
duplex auto
speed auto
interface GigabitEthernet0/1
ip address 192.168.11.1 255.255.255.0
duplex auto
speed auto
interface GigabitEthernet0/2
ip address 22.20.19.18 255.255.255.0
duplex full
speed 100
crypto map VZW_VPNTUNNEL
router bgp 65505
bgp log-neighbor-changes
network 0.0.0.0
network 192.168.11.0
neighbor 172.16.200.1 remote-as 6167
neighbor 172.16.200.5 remote-as 6167
ip forward-protocol nd
ip http server
ip http access-class 23
ip http authentication local
ip http secure-server
ip http timeout-policy idle 60 life 86400 requests 10000
ip route 0.0.0.0 0.0.0.0 22.20.19.19
ip access-list extended VZW_VPN
permit gre host 99.101.15.99 host 22.20.19.18
permit icmp host 99.101.15.99 host 22.20.19.18
permit esp host 99.101.15.99 host 22.20.19.18
permit udp host 99.101.15.99 host 22.20.19.18 eq isakmp
permit gre host 22.20.19.18 host 99.101.15.99
permit gre host 22.20.19.18 host 99.100.14.88
access-list 23 permit 10.10.10.0 0.0.0.7
control-plane
end
So after spending countless hours analyzing every portion of this, I think that adding one line to this will get it going (or at least closer).
ip route 192.168.1.0 255.255.0.0 22.20.19.19
That should allow my internal LAN to reach the Airlink gateways on the other side of the tunnel (I think)
Now for a couple of questions for those that are still actually hanging around.
#1 what is the purpose of the Ethernet address assigned to each tunnel? I only see them being used in the BGP section where they are receiving routing tables from the Verizon side (is that correct?). Why wouldn't or couldn't you just use the physical Ethernet address interface in its place (in the BGP section)?
#2 is the config above correct in pointing the default route to the physical Ethernet address? Does that force the packets into the tunnel, or shouldn’t you be pointing it towards the tunnel IP's (172.16.200.2)? If the config above is correct then I should not need to add the route I described above as if I ping out to 192.168.1.X that should catch it and force it into the tunnel where Verizon would pick it up and know how to get it to its destination??
#3 Will I need to add another permit to the VZW_VPN for TCP as in the end I need to be able to poll via Modbus which uses port 502 TCP. Or is TCP implicit in some way with the GRE permit?
I actually have alot more questions, but I will keep reading for now.
I really appreciate the time you all took to trudge through this. Also please feel free to point anything else out that I may have missed or that can be improved. Have a great day!

This post is a duplicate of this thread
https://supportforums.cisco.com/discussion/12275476/proper-routing-lan-through-verizon-private-network-gre-airlink-gateways
which has a response. I suggest that all discussion of this question be done through the other thread.
HTH
Rick

When do i have to use a gre over ipsec tunnel? i have heard that when i m using a routing protocol and vpn site to site i need a gre tunnel

i have configured a network with ospf and a vpn site to site without gre tunnel and it works very well. I want to know, when do i have to use gre tunnel over ipsec

Jose,
It sounds like you currently have an IPsec Virtual Tunnel Interface (VTI) configured. By this, I mean that you have a Tunnel interface running in "tunnel mode ipsec ipv4" rather than having a crypto map applied to a physical interface. In the days before VTIs, it was necessary to configure GRE over IPsec in order to pass certain types of traffic across an encrypted channel. When using pure IPsec with crypto maps, you cannot pass multicast traffic without implementing GRE over IPsec. Today, IPsec VTIs and GRE over IPsec accomplish what is effectively the same thing with a few exceptions. For example, by using GRE over IPsec, you can configure multiple tunnels between two peers by means of tunnels keys, pass many more types of traffic rather than IP unicast and multicast (such as NHRP as utilized by DMVPN), and you can also configure multipoint GRE tunnels whereas VTIs are point to point.
Here's a document which discusses VTIs in more depth: http://www.cisco.com/c/en/us/td/docs/ios-xml/ios/sec_conn_vpnips/configuration/xe-3s/sec-sec-for-vpns-w-ipsec-xe-3s-book/sec-ipsec-virt-tunnl.html#GUID-A568DA9D-56CF-47C4-A866-B605804179E1
HTH,
Frank

GRE Tunnel and static PAT

Hi to all,
I would like to know if it is possible to create a static Port Address Translation (PAT) that would translate a routable IP address to a private address where a GRE tunnel would end.
In other words, I am trying to see if we can use a static PAT for a GRE tunnel like the one that we can used to reach a HTTP server using a private IP address via static PAT to a routable IP address.
Just trying to see if it is possible to initiate a GRE tunnel from 192.168.1.1 (R1) and used 1.1.1.1 (R2), IP address reachable via internet, as destination address, in the case where we would do a PAT translation on R2 in order to actually terminate the tunnel on R3 router. The static PAT on R2 would translate 1.1.1.1 to 172.16.1.2.
I am basically looking for an equivalent to the following static PAT but for GRE tunnel
          ip nat inside source static tcp 10.10.10.5 80 192.168.2.1 80
Thanks for your help
Stephane

Hello Stephane,
GRE is neither TCP nor UDP, GRE has its own protocol number 47. You can allow the traffic by either by calling GRE instead of TCP or UDP or by just putting a normal IP static NAT entry.
Extended IP access list GRE
    10 permit tcp any any eq 47 log <--- No Hits
    15 permit tcp any any log          <--- No Hits
    20 permit udp any any eq 47 log <--- No Hits
    25 permit udp any any log          <--- No Hits
    30 permit gre any any log (20 matches)
    40 permit ip any any (43 matches)
*Mar 1 00:27:48.435: IP: tableid=0, s=10.10.10.2 (local), d=10.10.10.1 (Tunnel1), routed via FIB
*Mar 1 00:27:48.435: IP: s=10.10.10.2 (local), d=10.10.10.1 (Tunnel1), len 100, sending
*Mar 1 00:27:48.435:     ICMP type=0, code=0
*Mar 1 00:27:48.435: IP: s=192.168.9.5 (Tunnel1), d=192.168.8.2 (FastEthernet0/0), len 124, sending, proto=47
I hope it helps great for you. Please rate if you fell this is helpfull.
Thanks,
Kasi

GRE Tunnel/NAT with multiple subnets and interfaces

So, I am not sure if we are trying to accomplish too many things at once and what we are attempting to do is not possible or if we are missing something in our configurations...
Here is the situation...
We are migrating some equipment between datacenters. The equipment only a has a /27 worth of IP space assigned to it so we cannot simply "move" the IP space to the new datacenter. Further because we have several VPNs terminated in the old IP space that originate from devices we do not directly control and are essential in continuing to provide service, it was/is difficult to magically update some DNS entries and change IP addresses overnight. The last twist in this puzzle is that at the new datacenter, we will deploying some new equipment that will be in a separate subnet (with a separate Windows AD structure) but sharing the new public IP space we have in the new datacenter.
We thought using a GRE tunnel, some trunks, and a bunch of NATs would make the whole process easy and we tested ti in a lab and everything SEEMED to work. However, when we performed the move we ran into an odd issue that we were unable to figure out and had to go back to a failsafe configuration that has the essentials up and running, but the environment is not running in an ideal way for us to gradually transition as we would like.
Essentially what we had/have and how it was configured is as follows:
Site A
Edge Router - x.x.x.x /24 BGP announcement
x.x.x.y/27 that is within the /24 that we need at site b
GRE tunnel configuration
interface tunnel0
ip address 10.x.x.1 255.255.255.252
tunnel source <router edge IP>
tunnel destination <site b router edge ip>
keepalive 10 3
static route for site a public ip to bring it to site b via GRE tunnel
ip route x.x.x.y 255.255.255.224 10.x.x.2
Site B
Edge Router - y.y.y.y /24 BGP announcement
Similar GRE tunnel configuration (tunnel comes out and works so don't think issue is here)
2 Vlans (1 for site a ip space, 1 for site b ip space)
int vlan 50
ip address x.x.x.1 /27
int vlan 51
ip address y.y.y.129 /25
Trunk port for the VLANs going down to an ASA
int g1/1
swi mode trunk
swi trunk native vlan 51
swi tru all vlan 50,51
swi tru en dot1q
Then on the ASA, I have 2 physical interfaces for 4 logical interfaces (outside, outsideold, inside, insideold)
int e0/0
nameif outside
sec 0
ip address y.y.y.130 /25
int e0/0.50
nameif outsideold
sec 0
ip address x.x.x.2 /27
vlan 51
int e0/1
nameif inside
sec 100
ip address 192.168.y.1 /24
int e0/1.60
nameif insideold
sec 100
ip address 192.168.x.1 /24
vlan 60
A static route using the new ip space on the native outside interface...
route 0 0 y.y.y.129
And then I have some nat rules which is where I think things go a little haywire...
object network obj-y.y.y.0-24
subnet y.y.y.0 255.255.255.0
nat (inside,outside) dynamic interface
object network obj-x.x.x.0-24
subnet x.x.x.0 255.255.255.0
nat (insideold,outside) dynamic interface
object network obj-y.y.y.135-160
range y.y.y.135 y.y.y.160
object network obj-192.168.y.135-160
range 192.168.y.135 192.168.y.160
nat (inside,outside) static obj-y.y.y.135-160
object network obj-x.x.x.10-20
range x.x.x.10 x.x.x.20
object network obj-192.168.x.10-20
range 192.168.x.10 192.168.x.20
nat (insideold,outsideold) static obj-x.x.x.10-20
From some debugging and looking at packet-tracer, I found out I left out the below which was needed to properly nat traffic as it leaves the outside interface (when the default sends the traffic)
object network obj-192.168.x.10-20-2
range 192.168.x.10 192.168.x.20
nat (insideold,outside) static obj-x.x.x.10-20
There are / were a bunch of other nat exemptions for the VPNs and specific external routes to ensure all vpn traffic exited the "outsideold" interface which is where all the existing tunnels were terminated.
Everything appeared to be working great as all the VPN tunnels came up perfectly as expected and traffic appeared to be flowing, except for some of the most important traffic. The following was what was observed:
1. Any traffic using the dynamic NAT (ie...a machine with IP x.x.x.200 or y.y.y.20) would connect to the internet perfectly and work fine using the "new interface ip".
2. Any traffic in the "new range" using a one to one nat worked perfectly (ie y.y.y.140). Internet would work etc and nat translation would properly occur and everything could connect fine as expected.
3. ICMP packets to "old ip range" flowed perfectly fine to one to one nat IP (ie I could ping x.x.x.20 from outside) and likelise I could ping anywhere on the internet from a machine with a static natted ip.
4. Heres the butt...no traffic other than ICMP would reach these machines with static ips. Same range, same subnet as ones using the dynamic port translation that worked perfectly. Do not understand why this was / is the case and this is what I am seeking a solution to. I have attempted the following troubleshooting steps without success:
A. Confirmed MTU size was not an issue with the GRE tunnel. 2 methods, one plugging to edge router and using the "outsideold" ip space works perfectly and 2 if I assign outsideold ip space to "outside" interface, everything nats fine.
B. Ran packet-tracer, all results show "allow" as if I should be seeing the packets.
C. Confirmed local windows machine firewall was off and not blocking anything.
D. Reviewed logs and observed SYN timeouts and TCP teardowns as if the firewall is not getting a response and this is where I am stumped. There is no path around the firewall so asymmetric routing should not be an issue and if that was the problem it should not work when the "outsideold" ip space is assigned and natted from the "outside" interface, but it does. Packet-tracer shows proper nat translations occurring and there is definitely proper routing along the path for stuff to return to the network or ICMP would not work (IE I can ping www.google.com but not open the web page).
So what simple piece of the nat configuration am I overlooking because I cannot possible wrap my head around it being anything else.
Any suggestions / lessons would be greatly appreciated.

is this still a problem?

Ip route command in GRE tunnel

Hi Everyone,
I have setup GRE Lab between Routers R1 and R3.
R1 is connected to R2 using OSPF and R2 is connected to R3 using OSPF.
I config GRE tunnel interface on R1 and R3.
R1 has internal subnet say 100.x.x.x.x to share with R3.
R3 has internal Lan subnet say 101.x.x.x.x to share with R1.
Interesting traffic to pass through GRE tunnel is subnets 100.x.x.x. and 101.x.x.x.x.
R1 tunnel config
R1# sh run int tunnel 0
Building configuration...
Current configuration : 168 bytes
interface Tunnel0
ip address 13.13.13.1 255.255.255.0
keepalive 3
cdp enable
tunnel source Loopback0
tunnel destination 20.0.0.1
tunnel path-mtu-discovery
R3 Tunnel config
R3#sh run int tunnel 0
Building configuration...
Current configuration : 158 bytes
interface Tunnel0
ip address 13.13.13.3 255.255.255.0
keepalive 3 1
tunnel source Loopback0
tunnel destination 10.0.0.1
tunnel path-mtu-discovery
So my question is instead of using Routing protocols to advertise the Lan subnets from R1 and R3 can i use static routes?
for example
If i can use static routes say on R1
ip route 101.101.101.101 255.255.255 ?
what should be next hop IP here ?
tunnel interface of R3 Router or physical interface of R3 that connects to R2?
Then same way i can use static routes on R3 right ?
Thanks
Mahesh

Hello Mahesh,
You can use IP address as long as Tunnel IP addresses on both sides are in the same subnet. So in your case you can use
ip route 101.101.101.101 255.255.255 13.13.13.3
Or you can use the tunnel interface
ip route 101.101.101.101 255.255.255 Tunnel0
Although I have seen issues in some cases when the interface name is used instead of tunnel IP.
Please rate this post if helpful.
THanks
Shaml

Best way to pass IPv4 and IPv6 traffic over a GRE Tunnel

Hello,
We have two 3825 routers with Advanced Enterprise IOS 12.4.9(T). Each of them serves many IPv4 (private and public) and IPv6 networks on their respective site.
We have created a wireless link between the two, using 4 wireless devices, with IP Addresses 10.10.2.2, 3, 4, 5 respectively (1 and 6 are the two end Ethernet interfaces on the routers).
Then we created a GRE tunnel over this link using addresses 172.16.1.1 and 2 (for the two ends) to route traffic over this link.
Now we want to route IPv6 traffic over the same link. However, we found that simply routing the IPv6 traffic over the above GRE / IP tunnel did not work.
Questions:
Is there a way we can use the same (GRE / IP) tunnel to transport both IPv4 and IPv6 traffic?
If not, can we setup two GRE tunnels over the same wireless link, that is, one GRE / IP for IPv4 traffic and a second one GRE / IPv6 for IPv6 traffic?
In brief, what is the suggested way to transport IPv4 and IPv6 traffic over the aforementioned (wireless) link?
I have read http://www.cisco.com/c/en/us/td/docs/ios/12_4/interface/configuration/guide/inb_tun.html#wp1061361 and other Internet material, however I am still confused.
Please help.
Thanks in advance,
Nick

We have set up two tunnels over the same link, one GRE / IP for the IPv4 traffic and one IPv6 / IP ("manual") for the IPv6 traffic. This setup seems to be working OK.
If there are other suggestions, please advise.
Thanks,
Nick

Problem with a simple GRE tunnel

Hello everyone:
I have a problem with a simple GRE tunnel, and can not make it work, the problem lies in the instruction "tunnel source loopback-0" if I use this command does not work, now if I use "tunnel source <ip wan >" if it works, someone can tell me why?
Thanks for your help
Router 1: 2811
version 12.4
no service password-encryption
hostname cisco2811
no aaa new-model
ip cef
interface Loopback0
ip address 2.2.2.2 255.255.255.255
interface Tunnel0
ip address 10.10.1.1 255.255.255.0
tunnel source Loopback0
tunnel destination 217.127.XXX.188
interface Tunnel1
ip address 10.10.2.1 255.255.255.0
tunnel source Loopback0
tunnel destination 80.32.XXX.125
interface FastEthernet0/0
description LOCAL LAN Interface
ip address 192.168.1.254 255.255.255.0
ip nat inside
ip virtual-reassembly
duplex auto
speed auto
interface FastEthernet0/1
description WAN Interface
ip address 195.77.XXX.70 255.255.255.248
ip nat outside
ip virtual-reassembly
duplex auto
speed auto
ip forward-protocol nd
ip route 0.0.0.0 0.0.0.0 195.77.XXX.65
ip route 192.168.3.0 255.255.255.0 Tunnel0
ip route 192.168.4.0 255.255.255.0 Tunnel1
ip nat inside source route-map salida-fibra interface FastEthernet0/1 overload
access-list 120 deny ip 192.168.1.0 0.0.0.255 192.168.3.0 0.0.0.255
access-list 120 deny ip 192.168.1.0 0.0.0.255 192.168.4.0 0.0.0.255
access-list 120 permit ip 192.168.1.0 0.0.0.255 any
route-map salida-fibra permit 10
match ip address 120
Router 2: 2811
version 12.4
service password-encryption
ip cef
no ip domain lookup
multilink bundle-name authenticated
username admin privilege 15 password 7 104CXXXXx13
interface Loopback0
ip address 4.4.4.4 255.255.255.255
interface Tunnel0
ip address 10.10.1.2 255.255.255.0
tunnel source Loopback0
tunnel destination 195.77.XXX.70
interface Ethernet0
ip address 192.168.3.251 255.255.255.0
ip nat inside
ip virtual-reassembly
hold-queue 100 out
interface ATM0
no ip address
no ip route-cache cef
no ip route-cache
no atm ilmi-keepalive
dsl operating-mode auto
interface ATM0.1 point-to-point
ip address 217.127.XXX.188 255.255.255.192
ip nat outside
ip virtual-reassembly
no ip route-cache
no snmp trap link-status
pvc 8/32
encapsulation aal5snap
ip route 0.0.0.0 0.0.0.0 ATM0.1
ip route 192.168.1.0 255.255.255.0 Tunnel0
ip nat inside source route-map nonat interface ATM0.1 overload
access-list 100 permit ip 192.168.3.0 0.0.0.255 192.168.1.0 0.0.0.255
access-list 120 deny ip 192.168.3.0 0.0.0.255 192.168.1.0 0.0.0.255
access-list 120 permit ip 192.168.3.0 0.0.0.255 any
route-map nonat permit 10
match ip address 120

Hello, thank you for the answer, as to your question, I have no connectivity within the tunnel, whether from Router 1, I ping 10.10.1.2 not get response ...
Now both routers remove the loopback, and the interface tunnel 0 change the tunnel source to "tunnel source " tunnel works perfectly, the problem is when I have to use the loopback. Unfortunately achieved when the tunnel work, this will have to endure multicast, and all the examples found carrying a loopback as' source '... but this is a step back ..
Tunnel0 is up, line protocol is up
Hardware is Tunnel
Internet address is 10.10.1.1/24
MTU 1514 bytes, BW 9 Kbit, DLY 500000 usec,
reliability 255/255, txload 1/255, rxload 1/255
Encapsulation TUNNEL, loopback not set
Keepalive not set
Tunnel source 2.2.2.2 (Loopback0), destination 217.127.XXX.188
Tunnel protocol/transport GRE/IP
Key disabled, sequencing disabled
Checksumming of packets disabled
Tunnel TTL 255
Fast tunneling enabled
Tunnel transmit bandwidth 8000 (kbps)
Tunnel receive bandwidth 8000 (kbps)
Last input 09:04:38, output 00:00:19, output hang never
Last clearing of "show interface" counters never
Input queue: 0/75/0/0 (size/max/drops/flushes); Total output drops: 0
Queueing strategy: fifo
Output queue: 0/0 (size/max)
5 minute input rate 0 bits/sec, 0 packets/sec
5 minute output rate 0 bits/sec, 0 packets/sec
0 packets input, 0 bytes, 0 no buffer
Received 0 broadcasts, 0 runts, 0 giants, 0 throttles
0 input errors, 0 CRC, 0 frame, 0 overrun, 0 ignored, 0 abort
11101 packets output, 773420 bytes, 0 underruns
0 output errors, 0 collisions, 0 interface resets
0 unknown protocol drops
0 output buffer failures, 0 output buffers swapped out

GRE tunnel through asa no pptp, l2tp, ipsec

Hello!
can't understand how to configure GRE tunnel through ASA
i have one router with public ip, connected to internet
ASA 8.4 with public ip connected to internet
router with private ip behind ASA.
have only one public ip on ASA with /30 mask
have no crypto
have network behind ASA and PAT for internet users.
can't nat GRE? cause only TCP/UDP nated(?)
with packet-tracer i see flow already created but tunnel doesn't work

A "clean" way would be to use a protocol that can be PATted. That could be GRE over IPSec. With that you have the additional benefit that your communication is protected through the internet.
Don't stop after you've improved your network! Improve the world by lending money to the working poor:
http://www.kiva.org/invitedby/karsteni

Tcp mss adjust calculation for GRE tunnel over DSL line

hi guys,
need your advice on this one, as i search on cisco.com and netpro but unable to find the exact info that i required.
First, can anyone confirm the following calculation to find out MSS size.
Mss size = MTU size - encapsulation size - tcp header size
So for normal case;
MSS = 1500 - 48 (48 is the tcp/ip header)
so MSS = 1452
Thus in my case GRE tunnel over DSL connection;
MSS = 1492 - 24 - 48 (24 is the GRE encap; 48 is the tcp/ip header)
MSS = 1420
is this correct?
Secondly, where should the ip tcp mss-adjust to be implemented. Is it at the Dialer(DSL) interface or at Tunnel interface?

I don't use the math (it doesn't work for me probably b/c I miss something). Here's how I do it-
C:\>ping 10.125.0.250 -f -l 1600
Pinging 10.125.0.250 with 1600 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
C:\>ping 10.125.0.250 -f -l 1500
Pinging 10.125.0.250 with 1500 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
C:\>ping 10.125.0.250 -f -l 1400
Pinging 10.125.0.250 with 1400 bytes of data:
Reply from 10.125.0.250: bytes=1400 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1400 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1400 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1400 time=19ms TTL=251
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 19ms, Maximum = 19ms, Average = 19ms
C:\>ping 10.125.0.250 -f -l 1450
Pinging 10.125.0.250 with 1450 bytes of data:
Reply from 10.125.0.250: bytes=1450 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1450 time=20ms TTL=251
Reply from 10.125.0.250: bytes=1450 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1450 time=19ms TTL=251
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 19ms, Maximum = 20ms, Average = 19ms
C:\>ping 10.125.0.250 -f -l 1475
Pinging 10.125.0.250 with 1475 bytes of data:
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Packet needs to be fragmented but DF set.
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 0, Lost = 4 (100% loss),
C:\>ping 10.125.0.250 -f -l 1470
Pinging 10.125.0.250 with 1470 bytes of data:
Reply from 10.125.0.250: bytes=1470 time=19ms TTL=251
Reply from 10.125.0.250: bytes=1470 time=22ms TTL=251
Reply from 10.125.0.250: bytes=1470 time=20ms TTL=251
Reply from 10.125.0.250: bytes=1470 time=19ms TTL=251
Ping statistics for 10.125.0.250:
Packets: Sent = 4, Received = 4, Lost = 0 (0% loss),
Approximate round trip times in milli-seconds:
Minimum = 19ms, Maximum = 22ms, Average = 20ms
C:\>
1470 works and has a little bit of extra room. The tcp mss-adjust should be done on the LAN interface.
Hope it helps.

Interface Bridging Into GRE Tunnel

Hello all, I was wondering if it is still possible as I know it was never supported to bridge a layer 2 interface directly into a GRE tunnel. I have a customer that currently has a dedicated L2 circuit and a new L3 connection, he wants to move his L2 device to his L3 link to save money on circuits. The issue that I have is he does not want to change his IP addresses and the layer 2 network terminates in another location 20 miles away. The layer 3 routed network is also between both buildings and I can create a GRE tunnel between the 2 locations without touching the Internet. I have tried this using a 2921 router runnning IOS 15.4(2)T1 but the bridge-group command is not available on the GRE tunnel interface.
I have also looked at pseudowire and cannot find the commands related to this, do I need to upgrade my license to security?
Cheers
Stuart

It's a hidden command. Even do, you might get a warning messasge stating this is obsolete and unsupported, it still technically a valid configuration. Legacy, but works.
Keep in mind there are better solutions for this kind of connections. But you can try it, it's simple anyways.
Host1---Fa0/0--R1-------------GRE------------R2--Fa0/0---Host2
1. Create a Loopback intf. on both routers and ensure L3 connectivity between them.
2. Create bridge:
router(config)#bridge 1 protocol ieee
3. Create a GRE tunnel interface (dont configure IP's):
router(config)# interface tun0
router(config-if)# tun source loopback x
router(config-if)# tun destination <other router loopback ip>
router(config-if)# bridge-group 1
**This is a hidden cmd. You will get a warning message, but ignore it**
3. Attach Physical Interface to Bridge as well:
router(config)# interface Fa0/0
router(config-if)# bridge-group 1
4. Configure the Hosts IP addresses to be on the same IP Segment and validate communication between them.
You can try this on GNS3 as well. I made a diagram and a brief explanation at another thread, but really don't remember how to get to it.
Once again, this is legacy and there are better ways to achieve this. But for small implementations this is valid and easier. It also helps to understand the newer versions/enhancements to this as well.
HTH

GRE tunnel limitations

Similar Messages

Maybe you are looking for