MPLS MTU issue (diagram attached)

Unanswered Question
Jun 15th, 2008
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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



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guruprasadr Sun, 06/15/2008 - 06:07
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HI Haris, [Pls Rate if HELPS]


I beleive if your Interface @ Gi0/1 of 7206 is configured by any one way as below means it should work:


Option: I

MPLS-Router#sh run int Gi0/2

Building configuration...


Current configuration : 217 bytes

!

interface GigabitEthernet0/2

description TO SWITCH xxx.xxx.xxx.xxx

mtu 1526

no ip address

no ip mroute-cache

load-interval 30

duplex full

speed 1000

media-type rj45

no negotiation auto

no cdp enable

end


Option: II

MPLS-Router#sh run int Gi0/1

Building configuration...


Current configuration : 329 bytes

!

interface GigabitEthernet0/1

description to SWITCH

mtu 1526

ip address xxx.xxx.xxx.xx xxx.xxx.xxx.xx

ip route-cache flow

load-interval 30

duplex full

speed 100

media-type rj45

no negotiation auto

mpls label protocol ldp

tag-switching ip

end


Try to Increase the MTU size on SWITCH and see the possibility to enable the Jumbo Frame Option if applicable.


Check the same and Kindly Update. Hope i am Informaitve.


Pls RATE if HELPS


Best Regards,


Guru Prasad R

Harold Ritter Sun, 06/15/2008 - 06:16
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Haris,


I suppose the default MTU of 1518 on the Foundry device includes the ethernet header and checksum, which leaves 1500 bytes for the payload. This is not sufficient to carry 1500 bytes IP packets + the mpls label(s). Try increasing the MTU on the Big Iron.


Regards,

Haris P Sun, 06/15/2008 - 21:43
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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

Harold Ritter Mon, 06/16/2008 - 06:36
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Haris,


I would be very surprised if te BigIron didn't support jumbo frames. You should check for a command in global mode (not at the interface level) to enable jumbo frame support.


Regards,

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