Pruning ISL trunks question
Can you guys confirm this for me please ?
1. If I prune a vlan from an isl trunk when the end switch has no member ports, I will save isl encapsulated broadcast traffic from going across the trunk for this vlan ?
2. If I convert my trunks from isl to 802.1q I will save 26 bytes for each frame. Perhaps more because with 802.1q I could have a native non encapsulated vlan and save even more ?
Is this good practice ?
Thanks
Hi Friend,
1. Yes
2. ISL encapsulation does not have a concept of Native vlan so yes native vlan on dot1q trunk will not have any tagging and yes if you configure dot1q you will save a header of 26 bytes but dot1q also puts a internal tagging of 4 bytes.
Yes it is definetely a good practice because first dot1q is open standard and second farme size get reduced.
HTH, if yes please rate the post.
Ankur
Similar Messages
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ISL trunking and MTU and PMTUD
All,
In the case you setup a ISL trunk from switch to a router (using logical interfaces), does anyone know if the MTU changes on the routers interface and/or the router can cope with the 30 bytes overhead of ISL. I would think that the router can cope with the extra 30 bytes, but i do never see any baby giant frames (1514 + 30 = 1544 bytes frames) in the statistics.
GeertWhen a port is enabled for 802.1q trunking the switch will automatically assume that there is an extra four bytes of data appended on, incrementing the frame size of the Layer 2 (L2) packet. Therefore, for implementations that require exactly only one tag to be carried (either 802.1q or Multiprotocol Label Switching (MPLS), but not both), it is possible to force the switchport to accept an extra four bytes of data by configuring it as a trunk port.
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Hi,
I' ve got a theoretical question about the behaviour of ISL at Cisco MDS switches:
I heard, that during a transfer (a continuous sequence of frames) between a target and an initiator (each of them are on seperated switches, which are connected with only one ISL), no other end device can use the ISL. When the sequence of frames (same OX ID, RX ID) is transfered, another end device can use the ISL.
There is no "multiplexing" of the ISL.
Q1: Is this true?
Q2: If yes, what happend, if you tranfer a lot of data between one target & one initiator. Is there a congestion on the isl for all other devices?
Regards
MarkusMarkus,
The MDS doesn't transfer entire exchanges at a time on a given ISL. Meaning OXID1, OXID2 etc... It will transmit the frames as they arrive. Such that you could transfer over the ISL:
OXID1Frame1, OXID2Frame1, OXID1Frame2, OXID1Frame3
The second problem could occur in a situation in which the receiver's buffers were full and thereby the TX port on the switch egress frames out of the switch, then the Virtual Output Queue could fill up (for which there is one assigned to every input port for every output port) and eventually the TX side of the ISL would run out of buffers. To completely avoid this, you would need per flow buffer 2 buffer credits. As a note the number of and depth of VOQ was designed to help avoid this situation as explained in this whitepaper and illustrated below.
-Seth -
I have a network design issue to solve and need some help. Current network uses ISL to trunk vlans between two sites. Some encryption devices need to be installed that do not understand ISL (or BPDUs for that matter). I need to split the ISL, or tunnel it, so that the inside devices cannot see the L2 stuff but the end devices can still communicate. Any ideas?
Regards ... JohnHi Josh
I had to solve a very similar problem to yours, and the solution I came up with was to use L2TPv3 (layer 2 tunnelling protocol) over IPSEC. I used the same device (a pair of old 1700 series routers at each end) to create both the L2 tunnel and the IPSEC tunnel, but in your case you are using a separate device to do the encryption. You just need to create the L2 tunnel between 2 devices which are on the unencrypted side at each end. You need to ensure that the 2 devices can route to each other. -
Hello,
Quick question regarding VSAN trunking. I have 2 6120 Fabric Interconnects and 2 MDS 9148's. Fabric-A is connected to MDS-1 and Fabric-B is connected to MDS-2 (4 4Gb links).
I have created 3 VSAN's on the MDS's and have configured the ports connected to the Fabric interconnects to trunk mode (VSAN trunking). I want to create a fiber channel on the UCS for the 6120 connections down to the MDS. (I know I need UCS version 1.4 to do this).
I'm wondering if I need to add the fc ports on the 6120 (4 each) to any particular VSAN (or create a new VSAN), or once I create a fiber channel and bundle them then they will trunk with the MDS's without a problem?
I appreciate the help.
Thanks!The functionality you describe is exactly what is provided in the 1.4.1 release.
The only caveat is a issue with any existing VSANs DomainIDs on your UCS system that fall into the range of 3840 to 4078. If you attempt to enable trunking and have VSANs in that DomainID range you will receive a warning that those VSANs will become disabled. If you proceed, they will go disabled and no longer pass traffic. All other allowed VSAN DomainIDs will continue to function properly.
This is a recent changed that was introduced with the MDS NX-OS 4.1 code. Which the UCS shares with at 1.4.1 for fc trunk
Regarding your question regarding what VSAN to put the end ports into. As you'll be starting in NPV mode, it's best to ensure proper connectivity by having the UCS and MDS end ports in the same VSAN. This will establish the link up properly and eliminate later physical level troubleshooting.
In UCS, trunk is disabled by default, see above for reason. Enabling UCS trunk mode is at the switch level, all uplink ports will be trunk enabled. In the MDS trunk mode is enabled at the interface level (individual link or port-channel). Once trunking is enabled on both sides, all VSAN from the UCS side are allowed. The MDS side can be trimmed to allow specific or a range of VSANs. Default on MDS is all VSANs.
As to what is best practice for what VSAN to put those end ports into, is a subject to debate. My best practice is to use VSAN 1, as VSAN 1 can never be deleted, which means the SAN port-channel will never lose it's native port. -
1300 bridges trunking question
Hi all,
I have two 1300 bridges connecting two buildings. Both buildings are using native vlan. I only have one SSID and native vlan on the birdges. There is a L3 switch connecting to the root bridge and L2 switch connecting to the non-root bridge.
Right now, we are upgrading the network to support mutilple vlans. Do I need to make trunking on the bridges in order for the bridges to pass multiple vlans traffic? I already made trunking (802.1q) on both switches. But once I assign ports to access different vlan, I could not get dhcp address (except native vlan)if I am on the second building.
Any suggestion/comment?
thanks
GeneHey Gene,
I had a similar setup and the only thing you need to care about pretty much is that the native vlan in your bridges is the one assigned to the SSID which it linking those 1300 together... All the rest of the vlans at your switch will pass through the wireless link effortlessly... :)
Just try to be sure you are NOT restricting vlans at the switch port where you have your bridges connected.
If you need any assistance please do not hesitate in contact me... :)
Cheers,
Hery -
I have 2 switches set up as a VTP server and client. When I assign a vlan to a port on the server, is the same vlan always going to be assigned to the same port number on the client switch ? I have vlan 2-6 on ports 2-6 of the VTP server switch and see the same port assignment on the client switch when using show vlan. Is this how it is supposed to work ?
Your VTP server switch sends BPDU to your VTP client switch. The vlan's you create and port assignment you create on your server switch are propagated to your client switch. This is the correct action of the server client relationship, VTP is use mostly in large network to make vlan assignment easier and less chances for config errors. Each time you make a config change the revision number will increment by one, if a client switch receives a BPDU with a higer revision number than it's own, it will change it's config according to the info in the BPDU. You can place the client switch in transparent mode and it will forward BPDU but will not change config. You should look into vlan pruning or usingthe "vlan allowed" command.
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WRVS4400N VLAN trunking question
Hi all,
I just got a SRW224G4 today my main objective is to trunk 30 VLAN(s) to my WRVS4400N for interVLAN communication. So far I set G1 on my SRW as a trunk port and linked it to port 2 on my WRVS4400N (which is also set as a trunk).
So far no good when I go into LAN settings I do not see an option wheree I can set DHCP addresses or gateways for these VLAN(s). Is this even possible with the WRVS4400N I meen if Linksys is going to provide a small business solution atleast their equipment should support VLAN trunking with each other.
If anybody knows the solution to this please let me know.
CheersFrom what I know, although the WRVS4400N has support for port based VLAN setup, it does not give you the option to set different DHCP addresses for each of the 4 VLANS.
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SIP Trunk Question - Outbound Calls Fail
Hi Folks,
I am using a Cisco 2821 as a router that will convert a SIP trunk to an E1 PRI. Si my setup is:
SIp-Trunk > 2821 Router > E1 port on 3900> CUCM
Inbound calls are working fine, but outbound are failing. I am starting to think its due to transcoding issue on the SIP-GW maybe (there is nothing configured on it for XCODE etc).
I think my configuration is fine as I am able to recieve calls inbound. Just outbound fail.
Here are the debugs from the SIP-GW:
"Debug CCSIP calls"
*Nov 26 18:50:50 UTC: //929/F9E88693801B/SIP/Call/sipSPICallInfo:
The Call Setup Information is:
Call Control Block (CCB) : 0x4BB4F194
State of The Call : STATE_DEAD
TCP Sockets Used : NO
Calling Number : 1528xxxx
Called Number : 909
Source IP Address (Sig ): 172.29.x.xxx
Destn SIP Req Addr:Port : 10.200.7.157:5060
Destn SIP Resp Addr:Port : 10.200.7.157:5060
Destination Name : 10.200.7.157
*Nov 26 18:50:50 UTC: //929/F9E88693801B/SIP/Call/sipSPIMediaCallInfo:
Number of Media Streams: 1
Media Stream : 1
Negotiated Codec : No Codec
Negotiated Codec Bytes : 0
Nego. Codec payload : 255 (tx), 255 (rx)
Negotiated Dtmf-relay : 0
Dtmf-relay Payload : 0 (tx), 0 (rx)
Source IP Address (Media): 172.29.5.210
Source IP Port (Media): 16786
Destn IP Address (Media): -
Destn IP Port (Media): 0
Orig Destn IP Address:Port (Media): [ - ]:0
*Nov 26 18:50:50 UTC: //929/F9E88693801B/SIP/Call/sipSPICallInfo:
Disconnect Cause (CC) : 28
Disconnect Cause (SIP) : 484
Can anyone shed some light on the area that I need to focus on? This is my first attempt at SIP and I am confused :)
Thanks.Hi
909 is what I meant to dial as that is the help desk for the telco.
I tried mobile numbers as well getting the same error codes. And international numbers.
If it's based on the called number being wrong then I guess I will have to play with the calling party ID and call type as well... Maybe this is causing it to fail?? -
ISL Trunk Between Nexues 5596 & MDS 9222i_Limitation & Software
Hello,
Need to migrate MDS 9222i to Nexus 5596
anyone can point compatibility issues with software code?
thanksanything in here ?
http://www.cisco.com/c/en/us/td/docs/switches/datacenter/mds9000/interoperability/matrix/intmatrx.pdf -
When port on 3750 is in access mode (vlan 24), and port on 1912 is trunk off, everything is ok. But now I need to communicate the devices via ISL trunk. I had configured both machines by the appropriate tech docs, but i have troubles...
On 1912 machine:
ip address 10.195.60.2 255.255.255.0
ip default-gateway 10.195.60.1
interface FastEthernet 0/26
duplex full
trunk On
On 3750 machine:
interface GigabitEthernet2/0/20
description Trunk to Cisco 1912
switchport encapsulation isl
switchport mode trunk
no mdix auto
interface Vlan24
ip address 10.195.60.1 255.255.255.0
In this way configuration (trunking), there is no ping between them.
May be i do something wron? PLS HELP!Hm... now i had configured `Meri` on both devices. But still the same problem. May be trouble in the difference of VTP versions?
Statistics:
3750s#show vtp counters
VTP statistics:
Summary advertisements received : 0
Subset advertisements received : 0
Request advertisements received : 46507
Summary advertisements transmitted : 147343
Subset advertisements transmitted : 46516
Request advertisements transmitted : 0
Number of config revision errors : 0
Number of config digest errors : 0
Number of V1 summary errors : 0
VTP pruning statistics:
Trunk Join Transmitted Join Received Summary advts received from
non-pruning-capable device
Gi1/0/1 0 0 0
Gi1/0/2 0 0 0
Gi1/0/4 0 0 0
Gi1/0/8 0 0 0
Gi1/0/12 0 0 0
Gi2/0/5 0 0 0
Gi2/0/8 0 0 0
Gi2/0/15 0 0 0
Gi2/0/19 0 0 0
Gi2/0/20 0 0 0
Catalyst_1912#show vtp statistics
Receive Statistics Transmit Statistics
Summary Adverts 4 Summary Adverts 5
Subset Adverts 0 Subset Adverts 4
Advert Requests 0 Advert Requests 50
Configuration Errors:
Revision Errors 0
Digest Errors 0
VTP Pruning Statistics:
Port Join Received Join Transmitted Summary Adverts received
with no pruning support
A 0 0 0
B 0 0 0 -
Cisco 2950 Gigabit interface trunking
This is the small part of the network design that i want to seek advice from the forum .
++ we have two cisco 2950 switch
switch1 ==gigabit trunk == switch2 .
we want trunking to enable between these two two switches by using there gigabit ethernet interface ie
switch 1 interface GigabitEthernet0/1 is connected to switch 2 interface GigabitEthernet0/1 and switch 1 interface GigabitEthernet0/2 is connected to switch 2 interface GigabitEthernet0/2.
i need advice in following areas
++ what cable do we need to connect these switches (i guess cross over cable will do )
++ do we have configuration on the tech tip page
for achieving the same ?Hello,
for the trunk connection you need a four twisted-pair crossover cable:
Figure B-11 Four Twisted-Pair Crossover Cable Schematics for 10/100/1000 and 1000BASE-T Ports
http://www.cisco.com/en/US/partner/products/hw/switches/ps628/products_installation_guide_chapter09186a0080346679.html#wp1020386
You can either configure 802.1Q or an ISL trunks between your switches. For 802.1Q the configuration would look like this:
Switch1
interface GigabitEthernet0/1
switchport trunk encapuslation dot1q
switchport mode trunk
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport mode trunk
Switch2
interface GigabitEthernet0/1
switchport trunk encapuslation dot1q
switchport mode trunk
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport mode trunk
And for ISL encapsulation, the configuration would look like this:
Switch1
interface GigabitEthernet0/1
switchport trunk encapuslation isl
switchport mode trunk
interface GigabitEthernet0/2
switchport trunk encapsulation isl
switchport mode trunk
Switch2
interface GigabitEthernet0/1
switchport trunk encapuslation isl
switchport mode trunk
interface GigabitEthernet0/2
switchport trunk encapsulation isl
switchport mode trunk
You could also configure a GigaChannel to bind both interfaces into one logical link, for better throughput. For 802.1Q:
Switch1
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
interface GigabitEthernet0/1
switchport trunk encapuslation dot1q
switchport mode trunk
channel-group 1 mode on
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode on
Switch2
interface Port-channel1
switchport trunk encapsulation dot1q
switchport mode trunk
interface GigabitEthernet0/1
switchport trunk encapuslation dot1q
switchport mode trunk
channel-group 1 mode on
interface GigabitEthernet0/2
switchport trunk encapsulation dot1q
switchport mode trunk
channel-group 1 mode on
And for ISL:
Switch1
interface Port-channel1
switchport trunk encapsulation isl
switchport mode trunk
interface GigabitEthernet0/1
switchport trunk encapuslation isl
switchport mode trunk
channel-group 1 mode on
interface GigabitEthernet0/2
switchport trunk encapsulation isl
switchport mode trunk
channel-group 1 mode on
Switch2
interface Port-channel1
switchport trunk encapsulation isl
switchport mode trunk
interface GigabitEthernet0/1
switchport trunk encapuslation isl
switchport mode trunk
channel-group 1 mode on
interface GigabitEthernet0/2
switchport trunk encapsulation isl
switchport mode trunk
channel-group 1 mode on
HTH,
GP -
Is is a good idea to enable VLAN pruning on switch stacks or does this add to more CPU usage which could cause other problems. The network consists of 3750,3500 and 2900 switches.
Hi,
Pruning unneeded vlans off of trunks is a good idea, and may actually lower your CPU utilization, as the number of STP instances may be reduced as well.
From the best practices doc:
http://www.cisco.com/en/US/products/hw/switches/ps700/products_white_paper09186a00801b49a4.shtml
"VLANs can be pruned from trunks down to switches that do not have ports in the VLAN. This results in frame flooding that is more bandwidth-efficient. Manual pruning also has a reduced spanning-tree diameter. A per-switch VLAN configuration also encourages this practice."
HTH,
Bobby
*Please rate helpful posts. -
I have a 2950T-48-SI, a 3508G-XL, and a 3548-XL.
The 2950T and the 3508 are connected via Gig0/1 on the 2950 and Gig0/7 on the 3508.
The 3548 and the 3508 are connected via Gig0/1 on the 3548 and Gig0/1 on the 3508.
I have been using only the default VLAN for all of my devices. I now want to add a new VLAN (#10) and I want to be able to move each workstation port to a specific VLAN as needed.
Devices on the 2 VLANS do NOT need to communicate with each other and each VLAN has its own router.
Ive created the new VLAN on all switches. The VLAN10 router is connected to the 2950, as is a port in my office. When I assign that port in my office to VLAN10, I get a DHCP address from my VLAN10 router and I get out to the world correctly (through the VLAN10 router and not the VLAN1 router). So I know that the basic VLAN10 is working properly, getting to the correct router, etc.
The problem comes when I try to reconfigure the remote switches (the 3508 and the 3548) to use the new VLAN (in addition to the default VLAN). I can get the 3548 to talk to the 3508 correctly on VLAN10, but I cant get the 3508 to talk to the 2950 on VLAN10.
The options for Administrative Mode and Administrative Encapsulation on the Gigabit ports are different on the 2950 switch than they are on the 3500XL series, and I guess I dont know how to set them up correctly.
On the 2950, the only Administrative Encapsulation choice is 802.1Q. The Administrative Mode choices are:
Static Access
Dynamic Access
Dynamic Desirable
Dynamic Auto
802.1Q Trunk
802.1Q Trunk NonNegotiate
On the 3508 and 3548, the only Administrative Encapsulation choice is ISL. The Administrative Mode choices are:
Static Access
Multi-VLAN
Dynamic Access
ISL Trunk
802.1Q Trunk
It seems like the Encapsulation settings should match on both ends, but that doesnt seem to be possible on these switches
Can someone help educate me ?
Thanks, SusanHi Susan,
The encapsulation settings need not be same through out the network and it should be same on 2 oints connected to each other.
Yes 2950 only supports dot1q
So when you connect 2950T and the 3508 via Gig0/1 on the 2950 and Gig0/7 on the 3508 you can use dot1q encapslation and just issue a command
switchport mode trunk
When you connect 3548 and the 3508 via Gig0/1 on the 3548 and Gig0/1 on the 3508 you can also use dot1q trunk or ISL trunk your wish but better to use dot1q.
config t
interface interface_id
switchport mode trunk
switchport trunk encapsulation dot1q
If you issue this config on all the switches connected to each other it should definetely form a trunk.
Only thing is when you put this commands on 2950 switch need not put dot1q as it only supports dot1q
config t
interface interface_id
switchport mode trunk
HTH, if yes please rate the post.
Ankur -
Vlan 1 Pruning eligibility C3750-V2
I am looking for clarification of vlan pruning; I have seen documentation that leads me to understand that vlans 1,1002-1005 are not eligible for vlan pruning as it carries management traffic such as CDP, so even if a switch has no active vlan 1 ports and the trunk native vlan has been changed vlan 1 will still not be pruned from the trunk.
This is an offshoot from a problem I raised in the following discussion in which vlan 1 is being pruned from trunks connected to a C3750-V2 but not when connected to a C3750:
https://supportforums.cisco.com/discussion/12272906/spanning-tree-root-bridge-dispute-c3750-v2
IOS version: 15-0-2.SE5That is correct. However on the old 3750 stacks there are no active vlan 1 ports and the native vlan has been changed and vlan remains in a forwarding state. I thought the default vlan always stayed in a forwarding state, part of the reason vlan 1 cannot be deleted, to handle management traffic such as cdp (cdp is working across the trunk). I guess that makes it impractical to ever change the native vlan and a problem if you have security people who still believe vlan hopping is more than a theoretical threat. (As an after thought turning off VTP pruning also fixes the problem)
Thanks for responding
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