MPLS MTU size

Hello,
Please correct me if I am wrong. The MPLS MTU size is 1518 to 1520 and the normal MTU size is 1500, So does it means that while configuring the MPLS network on the Switches attached with the MPLS CE router we MUST have to configure the MTU size to 1520 or not.
Please confirm

MPLS is not configured between the CE and the PE. So if your IP mtu is 1500 then the switch between the CE and PE needs to support 1500 only.
The mpls mtu needs to be configured in the core where ethernet switches are used.
Hope this helps,

Similar Messages

MPLS MTU issues

Hello I am facing a strange issue and would be grateful to have any advice on this please.
I have an existing setup where Site A and site B are connected within an MPLS setup:
When I ping from Site B to site A with size 1500 it works no problem
ping vrf Data1 192.168.230.2 size 1500
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 192.168.230.2, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 496/496/500 ms
there is a new site C that has come up with a new link as a back up of site B but when i ping it only allows ping of 1496 and not anything more.
ping vrf Data1 192.168.230.2 size 1496
Type escape sequence to abort.
Sending 5, 1496-byte ICMP Echos to 192.168.230.2, timeout is 2 seconds:
Success rate is 100 percent (5/5), round-trip min/avg/max = 500/502/504 ms
ping vrf Data1 192.168.230.2 size 1497
Type escape sequence to abort.
Sending 5, 1497-byte ICMP Echos to 192.168.230.2, timeout is 2 seconds:
Success rate is 0 percent (0/5)
I have compared the configs and they are setup with same MPLS mtu size show as follows
Site B
interface FastEthernet2/0
no ip address
duplex full
speed 100
mpls label protocol ldp
mpls ip
mpls mtu 1524
end
Site C
interface FastEthernet0/1
no ip address
ip flow ingress
load-interval 30
duplex full
speed 100
mpls label protocol ldp
mpls ip
mpls mtu 1524
end
I have asked the provider of the circuit and they say that the MTU sizes on their devices are 1530 same as the link from site B because the switches connected to both the above routers have system MTU as 1530.
I cannot find out what the issue could be ?
any help on this will be much appreciated.
many thanks in advance.

Site A is 7206
Site B is 7206 and
Site C is 2811
1) Directions failing is both directions
When i debug the ip icmp echo
it comes back on Site A router as
*Oct 24 14:08:57.872 UTC: ICMP: dst (10.181.0.1) port unreachable rcv from 10.181.3.105
the utilization on Site C is as follows: could it be a reason why large sized packets are failing?
100 ** *       * ** * * *    * *      *   *         *        *   **     *
90 ** *       * ***** * *    * *      * *** *      * *      *   ****   *
80 #******    ** **###** **   ****      ****#*** *   ****     ** *##** **
70 #####***   ** *######********#**   * **####***#*****#**    ** *###***##
60 #######********###########*#####*******###############*** ****#########
50 ##########**#####################***####################******##########
40 ########################################################################
30 ########################################################################
20 ########################################################################
10 ########################################################################
   0....5....1....1....2....2....3....3....4....4....5....5....6....6....7..
             0    5    0    5    0    5    0    5    0    5    0    5    0
                   CPU% per hour (last 72 hours)
                  * = maximum CPU%   # = average CPU%
I have checked the configs and compared with the Site B configs and they seem to good. I have validated with someone else as well.
How do I check if there are places where more than one label is being used?

With MPLS - No Fragmantation with MTU Size 1501-1504

Ping with MTU 1500 and 1505 is OK.
Ping with MTU 1501-1504 doesn?t work - there is no fragmantation done.
This occures on a Cisco7200 and Cisco7500 where traffic is sended via a labeld switch path: MTU-Size from the Fast/Gig Eth-Interface is set to 1500. With no MPLS "no mpls ip" everthing works fine.
Does anyone have a solution for this?
Thanks and Regards
Erich

Hello,
did you configure "mpls mtu 1512" on all MPLS enabled interfaces? F.e.:
interface FastEthernet0/0/0
mpls mtu 1512
This would allow for as much as 3 labels.
There is no fragmentation for labeled packets, only for IP. So this could be a software/hardware bug as well.
Hope this helps! Please rate all posts.
Regards, Martin

Confused about mpls mtu command

hi,
i confuse about mpls mtu command
test platforms are 76 pfc3b,mpls,gigabit sip400 spa interface
if i didn't config mpls mtu command ,using default,ping command is successful,if more than 1496 packets, i can see fragment from show ip traffic.
if i config mpls mtu override 1504,ping command is sucessful too. there is fragment too when i use 1501 byte packet.
if i config mpls mtu override 1524 byte.
ping command failed if i use packet more than 1500, , all packet are droped,even 1501 byte.only 1500 byte packet can success.
all config above interface mtu is 1500.
this confused me.
why i use default 1500 interace mtu, mpls mtu override 1504 ,ping packet can fragment,ping success, but i use mpls mtu override 1524, i can see fragment in show ip traffic,but ping command failed. i can't see packet in destination router,how this work.
thank you!
jun

topology is simple
7609-1--sip GE spa----7609-2--pos---7609-3--flexwan E1-----7604-1--ge--ce
i config mpls mtu 1524 between 7609-1 and 7609-2 . and keep interface mtu 1500 default.
ping packet from 7609-1 to 7604-1 loopback 0.
ping 1500 byte packet is ok, but ping 1501 byte packet is totally lost.then i config mtu 1524 between 7604-1 and 7609-3, it is useless,notwork, i can't see packet coming from 7609-1 on 7604-1.
but i add config mtu 1524 between 7609-1 and 7609-2. config mtu 1500 between 7604-1 and 7609-3,ping 1501 bytes from 7609-1 to 7604-1 loopback0 is ok. but i can see fragment from show ip traffic command in 7609-3.
i have a question, why we need mpls mtu command. if we don't change interface mtu,just only config mpls mtu 1524, it doesn't work, if we just change mpls mtu,how it work in the ios. if we config interface mtu 1524,interface mtu size is big enough, it seems mpls mtu command is useless, we don't need mpls mtu command, just interface mtu 1524 is ok.
why we need mpls mtu command. we just only change interface mtu is enough.
thank you!
jun

6506 - SUP720-3B MTU size

Due to MPLS environment on our WAN, we need to increase MTU size on the lan.
We configure 6500 to use only layer 2 interfaces (switchport activate on each interface)
Do i need to configure MTU size on each interface (i think i need to do it if i want to use this interface at layer 3) or can i configure only global MTU (system jumbomtu 9216)
Is there a command to verify jumbomtu size set on the switch ?

you can use the MTU per VLAN on the 6500.
'set vlan 10 mtu "576-18190"' (catOS)
or
'vlan 10'
'mtu "1500-18190"' (IOS)
this command sets the MTU for VLAN 10; values are from 576 to 18190.
please see the following link for more info: (IOS)
http://www.cisco.com/en/US/products/hw/switches/ps708/products_command_reference_chapter09186a00801eaeec.html#wp1011172
please see the following link for more info: (catOS)
http://www.cisco.com/en/US/products/hw/switches/ps708/products_command_reference_chapter09186a00802debd1.html#wp1027906

MPLS MTU on FE interfaces with fixed interface MTU

What is the recommendation for setting MPLS MTU when the hardware does not permit the setting of the interface MTU:
PE-Edge-2(config)#int fastEthernet 0/0
PE-Edge-2(config-if)#mtu 1524
% Interface FastEthernet0/0 does not support user settable mtu.
The MPLS MTU could be changed with "mpls mtu 1524", but this gives the error:
PE-Edge-2(config-if)#mpls mtu 1524
*Dec 24 20:54:43.467: %TFIB-3-MPLS_MTU_SET: Setting mpls mtu to 1524 on FastEthernet0/0 which is higher than the interface mtu 1500 . This could lead to packet forwarding problems including packet drops.
Is it permissible to set the MPLS MTU greater than the interface MTU, as I thought that MPLS packets cannot not be fragmented, but rather simply dropped?
In this scenario, is the only solution to limit the size of inbound packets with something like "ip tcp adjust-mss 1476" to avoid any potential packet drops?

if your doing AToM then you have to change the mpls mtu in order to transport full frames over your backbone. I have the same issue with the mtu and setting the mpls mtu to 9196 while leaving the mtu at 1500 did not impact regular traffic at all but it did allow our l2vpn's to function correctly.

MPLS MTU problem

Hey Guys,
We currently have several remote sites that connect back to our core (7206vxr) via p2p t1's. One Site connects back to us via MetroE. All Sites are setup under 1 vrf. The sites that have t1's can ping each other with no problem even bumping the datagram size up to over 1000. The problem I'm running into is with the MetroE site. If I try and ping it or ping from the site and bump the datagram size up to 250 or higher the success rate goes down to about 30%. This in turn seems to be causing some issues with our clients. Any advice on this would be great. The setup is all the interfaces that connect to the remote sites are in the same vrf. We then run EIGRP and route the subnets needed and everything works great besides a few applications that seem to be related to something with the MetroE,MPLS, and MTU size, I just not sure where to start.
Thanks in Advance

Ok I tried this 3 times and upped the DG size by 100 each time. At 300 I started getting packet loss. The thing I don't understand is when setting the "Set DF bit in IP header" to yes I don't notice any differnce than when it's set to No.
TX-OPT-RTR#ping
Protocol [ip]:
Target IP address: 192.168.0.254
Repeat count [5]: 10
Datagram size [100]:
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 10, 100-byte ICMP Echos to 192.168.0.254, timeout is 2 seconds:
Packet sent with the DF bit set
Success rate is 100 percent (10/10), round-trip min/avg/max = 32/32/32 ms
TX-OPT-RTR#ping
Protocol [ip]:
Target IP address: 192.168.0.254
Repeat count [5]: 10
Datagram size [100]: 200
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 10, 200-byte ICMP Echos to 192.168.0.254, timeout is 2 seconds:
Packet sent with the DF bit set
Success rate is 100 percent (10/10), round-trip min/avg/max = 32/32/36 ms
TX-OPT-RTR#ping
Protocol [ip]:
Target IP address: 192.168.0.254
Repeat count [5]: 10
Datagram size [100]: 300
Timeout in seconds [2]:
Extended commands [n]: y
Source address or interface:
Type of service [0]:
Set DF bit in IP header? [no]: y
Validate reply data? [no]:
Data pattern [0xABCD]:
Loose, Strict, Record, Timestamp, Verbose[none]:
Sweep range of sizes [n]:
Type escape sequence to abort.
Sending 10, 300-byte ICMP Echos to 192.168.0.254, timeout is 2 seconds:
Packet sent with the DF bit set
Success rate is 70 percent (7/10), round-trip min/avg/max = 32/33/36 ms

MPLS MTU issue (diagram attached)

Dear Experts ,
I'm trying to run MPLS between two 7206 vxr router which is connected behind a Foundry Big Iron L3 router which is configured as a L2 device .
I put on my 7206 as
int gi0/1
ip address 172.16.14.1 255.255.255.0
mpls ip
mpls mtu 1526
But it seems that there is tag assiging ,but traffic like https didn't work after that . is there is any clue ?
Regards
Haris

Hi ,
There is no way to increase the MTU size on foundry . But it's giving me some error
BigIron1(config-if-e1000-1/8)#ip mtu 1526
Error - 1526 not between 576 and 1500
BigIron1(config-if-e1000-1/8)#mtu ?
Unrecognized command
How can know that whether the foundry supporting giant packets / not ? . I think it's not supporting giants , the following is the output of ping sweep from one cisco router to other one .
If it's not supporting giants what will happens to my mpls packets with size 1508 ? . Is it possible me to put the command "mpls mtu 1500" ,so that mpls mtu will limit to 1500
router1#ping
Protocol [ip]:
Target IP address: 213.12.90.1
Repeat count [5]: 1
Extended commands [n]: y
Source address or interface: 213.12.83.137
Set DF bit in IP header? [no]: y
Sweep range of sizes [n]: y
Sweep min size [36]: 1450
Sweep max size [18024]: 1550
Sweep interval [1]:
Type escape sequence to abort.
Sending 101, [1450..1550]-byte ICMP Echos to 213.12.90.1, timeout is 2 seconds:
Packet sent with a source address of 213.12.83.137
Packet sent with the DF bit set
Success rate is 45 percent (46/101), round-trip min/avg/max = 20/44/120 ms
the ping is same with and without DF bit set after enabling MPLS . But before enabling tag switching as I remember I was able to ping without DF Bit set
Regards
Haris

IPv4 Backbone Baby Jumbo MTU size - any adverse effect?

Hello.
Is there any complication or adverse effect, setting IPv4/MPLS backbone GE link MTU size bigger than the Ethernet De facto of 1500, in the ASR9000 IOX-XR 4.3.x? What would be practical size? 4470, 8192? We have customers request to set 1800 but too odd value. What is the value the ASR9K (Trident LC with RSP, not 440) and LCs supports?
Much appreciate for your support.
Thanks,
Intopian.

That is correct Won, there are other advantages also as you noted.
For routing protocols:
OSPF uses it to fill its DBD's do both sides need to ahve the same MTU size,
same applies to ISIS.
RIP doesnt really care, although it can pack more updates in a single packet
BGP, using TCP, will use the MTU to adjust its MSS value so BGP benefits from this also big time.
As for delay on voip, yes theoretically, if the link speed is low enough, serialization delay of a large mtu packet may induce jitter on the high priority voip packet. But with 1500 bytes, the "fragment" size should be adjusted at 750k (so half T1 speed) only. With the majority circuits operating now at 1G, 10G etc, this fragment size requirement is almost no longer there as the serialization delay is so low at these speeds.
Other then very low end CPE's or very old devices that dont like larger MTU's (eg very old PA's in the 7200) there is really no worry anymore increasing the MTU size.
I dont think there is a formal doc on this, but I am sure if google it, you can find recommendations from other folks
on what they have done/seen etc.
regards
xander
Xander Thuijs CCIE #6775
Principal Engineer
ASR9000, CRS, NCS6000 & IOS-XR

Why we need mpls mtu command?

if interface mtu is not big enough to take mpls packet. we just increase interface mtu. why we need mpls mtu command.
if we just only increase mpls mtu.there is problem if mpls mtu biger than interface mtu. so it seem mpls mtu command is useless.
why we need mpls mtu command!
thank you!
Jun

Hi,
i test it in netowork,like this\
topology is simple
7609-1pe--sip GE spa----7609-2p--pos---7609-3p--flexwan E1-----7604-1pe--ge--ce
i config mpls mtu 1524 between 7609-1 and 7609-2 . and keep interface mtu 1500 default.
ping packet from 7609-1 to 7604-1 loopback 0.
ping 1500 byte packet is ok, but ping 1501 byte packet is totally lost.then i config mtu 1524 between 7604-1pe and 7609-3, it is useless,not work, i can't see packet coming from 7609-1 on 7604-1.
then i add config mtu 1524 between 7609-1pe and 7609-2. config mtu 1500 between 7604-1 and 7609-3,ping 1501 bytes from 7609-1 to 7604-1 loopback0 is ok. but i can see fragment from show ip traffic command in 7609-3.
i have a question, why we need mpls mtu command. if we don't change interface mtu,just only config mpls mtu 1524, it doesn't work, if we just change mpls mtu,how it work in the ios. if we config interface mtu 1524,interface mtu size is big enough, it seems mpls mtu command is useless, we don't need mpls mtu command, just increase interface mtu 1524 is ok.
why we need mpls mtu command. we just only change interface mtu is enough.
when i config mpls mtu override 1524,this is a warning in ios:
Setting the mpls mtu to 1524 on interface serial1/0/0:0, which is higher than the interface MTU
1500. This could lead to packet forwarding problems including packet drops.
You must set the MPLS MTU values equal to or lower than the interface MTU values.
thank you!
jun

Is it MPLS mtu problem ?

Our compny is serviceing Mpls between HQ and Branch. PE<->PE is running EBGP through ppp multilink and PE<->CE is running OSPF.The PE router is a cisco 3845.When I configure, it is working well. In case CE<->CE, I can a ping each other, but I can not access web-server from Branch 2day later. I thought it is MTU problem,So that is way I have changed PE<->PE mtu size as 1526 and CE<->CE 1436. It was working well web-server,FTP at time. What am I asking you, I can access some kind of file.
Do I have to re-adjust Mtu size ? If do I have to do, which position do I have to do it ? Let me know. I am in serious.

Hi,
You might have a MTU issue, but maybe not in the MPLS environment.
Usually hosts are connected to the network through ethernet and have a MTU of 1500 Bytes. Thus your CE setting of 1436 Bytes might create your observed problem. The CE router might have to discard packets above 1436 with DF bit set.
MPLS adds 2 labels, i.e. 8 Bytes. With your settings this should create no problem (1436+8=1444 < 1526).
The general recommendadtion thus is: CE <-> CE should be 1500 Byte and inside the MPLS network you should adjust MTU to allow this.
Example:
CE:
interface Serial0
description to PE Serial1/0
mtu 1500
PE:
interface Serial1/0
description to CE Serial0
mtu 1500
interface Serial1/1
description to MPLS cloud
mtu 1526
mpls ip
To localize your problem I would use an extended ping with df bit set and varying sizes. You should get 1436 Bytes with your current settings. Increase this to 1500 Bytes MTU and test again. Finally you should be able to rule out network related issues - there might still be application related issues like file access restrictions on the server.
Hope this helps! Please use the rating system.
Regards, Martin

MTU Size Issue on Cisco 3560 Switch

Could anybody tell me how to change MTU Size on a Cisco 3560 Switch.i mean to say whether it is to be changed on FastEthernet Interfaces or on VLAN 1 or on Global Configuration Mode and with which Command to change it.

I am using MPLS on my Routers and the MTU size i have set on my Router Interfaces is 1524.
When i do a normal ping from Customer's one site to another (where my Traffic has to pass through this Switch VLAN)i get a reply , but when a Ping with a Byte Size of 1500 or more the Packets get completely dropped.
I think due to MTU Mistach bet. Switch and Router the Packets r getting droped,that is why i was trying to change it.
could the Packets get dropped because of this reason.Please suggest.

MPLS MTU on various ethernet controllers

Is there some documentation available which router ethernet interface controller supports which maximum frame size ?
Background:
We have some intra-PoP crossover FE connections in an MPLS VPN based network. To avoid fragmentation we'd like to increase the mpls mtu to e.g. 1520bytes. I know that this isn't an issue on a PA-2FE-TX (7206-VXR), but there are also c3745 used as PE / P boxes. Does anybody know what frame sizes the onboard FEs of the 3745 and the NMs of these platforms (e.g. NM-2FE2W) can support ?
There is a document available for switches on CCO:
http://www.cisco.com/warp/public/473/148.html
Something in that style whould be great ...
thanks,
Stefan

Any update on this ?

MPLS MTU Issue with PA-FE-TX

Dear All,
I got an ethernet backbone that do not support jumbo frame. The backbone connected my Cisco7206/NPE-G2 and Cisco7507 on each side.
The topology as below:
Cisco7206-Gi0/1<---Ethernet--->Cisco7507-F5/1/0.50 (I am using 802.1q sub-interface)
The config as below:
interface GigabitEthernet0/1
bandwidth 4000
ip address 10.86.40.2 255.255.255.252
no ip redirects
no ip proxy-arp
ip ospf network point-to-point
ip ospf cost 10
ip ospf mtu-ignore
load-interval 30
duplex full
speed 100
media-type rj45
negotiation auto
mpls label protocol ldp
mpls ip
mpls mtu 1508
end
interface FastEthernet5/1/0.50
encapsulation dot1Q 50
ip address 10.86.40.1 255.255.255.252
no ip redirects
no ip proxy-arp
ip ospf network point-to-point
ip ospf cost 10
ip ospf mtu-ignore
mpls label protocol ldp
tag-switching mtu 1508
tag-switching ip
end
interface FastEthernet5/1/0
description Trunk
no ip address
load-interval 30
full-duplex
end
The problem is when i using "ping vrf NM_TEST x.x.x.x size xxxx", the maximum size can only up to 1498byte. I have increase all of my switchs MTU to 1530, but also cannot ping with 1500byte. Is there any way can help to solve the problem?
Thanks for your kindly help!
Regards

Hi Mohamed,
Its all about the implementation, with AToM, VPLS, MPLS TE, MVPN and any relatively new technology that is still being developed and enhanced you must take care about the vendors' implementations and which standards and RFCs is it complying with and to what level. I've seen codes that do fragmentation for AToM and codes that don't, codes that support out of order recovery and codes that don't. But in the end the RFCs and standards are there, whether you are using a code that supports what you need or not is your call.
Well, taking the AToM fragmentation and reassembly for example, I quote from "RFC 4623 Pseudowire Emulation Edge-to-Edge (PWE3) Fragmentation and Reassembly" : "Fragmentation takes place in the transmitting PE immediately prior to PW encapsulation, and reassembly takes place in the receiving PE immediately after PW decapsulation.", in brief it uses the B and E bits in the control word as well as the sequence number, and since the control word is imposed on the ingress PE and then processed on the egress PE, thus the ingress PE would be capable of fragmentation and the egress PE would be capable of reassembly, again its all about the code you are running.
Now to the 1530 MTU point, again I'll take an AToM case (more specifically EoMPLS), the Core MTU must be equal or greater than the summation of: Edge MTU (1500:IP) + Transport Header (14:Ethr + 4:assuming dot1q) + Control Word (4) + MPLS Label Stack (4:LDP + 4:VC), which gives a total of 1530. I believe that the reason behind choosing the value of 1530 in the new codes lies in the fact that it is the most common highest MTU seen in practice, although a value of 1534 is required if EoMPLS VLAN + TE FRR is used, but anyway the MPLS MTU is user settable up to 1580.
I hope that I've been informative.
BR,
Mohammed Mahmoud.

Mid 2010 Macbook Pro - Change MTU size kills internet (Jumbo Frames)

Hi everyone, i'm hoping someone here can enlighten or help me solve my problem I'm having.
I am trying to change my MTU size to enable Jumbo frames on my 13 inch Mid 2010 Macbook Pro. I recently bought a ReadyNAS Ultra and would like to speed up transfers to the unit.
My setup is as follows:
I have my ReadyNAS Ultra 2 and 2010 Macbook Pro (Core 2 Duo) wired via cat6 ethernet to my 5th Generation Apple Airport Extreme. The Airport Extreme is connected via cat5e to my AT&T Uverse Gateway which is set up to allow my Airport to assign DHCP and NAT (gateway is in bridge mode with wireless off).
Anyways, I have enabled Jumbo frames on my ReadyNAS, when I enable them on my MBP.. it applies fine. It disconnects / reconnects the ethernet like it should, but then my connection drops. I can't see any devices on my LAN and I cannot access any internet websites, but according to the network pane I am still assigned a valid dhcp address. When I manually try to increase my MTU size, the same thing happens (from 9000 to 1600 I tried every size).....
Could it be my MBP just can't suppose the increase of MTU size? It leaves them at 1500 when I set it to automatic... if it doesn't support the increased MTU size, why would it let me custom change the MTU and even give an option to select "Jumbo Frames (9000)"?
I appreciate any help in advance!!

asdftroy wrote:
If you did read my post then you would have saw that the option is there, but that is not entirely what my inquiry is about. The option isn't working as intended, and I was wondering if anyone had the same issues as me. Thanks anyways.
Anyone else?
The way you responded to someone trying to help you probably means others will be hesitant to try.

MPLS MTU size

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