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Bronze

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

4 REPLIES

Re: MPLS MTU issue (diagram attached)

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

Cisco Employee

Re: MPLS MTU issue (diagram attached)

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,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
Bronze

Re: MPLS MTU issue (diagram attached)

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

Cisco Employee

Re: MPLS MTU issue (diagram attached)

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,

Harold Ritter
Sr. Technical Leader
CCIE 4168 (R&S, SP)
harold@cisco.com
México móvil: +52 1 55 8312 4915
Cisco México 
Paseo de la Reforma 222 Piso 19
Cuauhtémoc, Juárez
Ciudad de México, 06600
México
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