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P-to-P load sharing ?

thedquoc
Level 1
Level 1

My 2 core routers have total 3 links . Now I want them to enable MPLS ip on their interfaces as P routers, but I am not sure if I should enable on all 3 pairs of interfaces and how it loads sharing MPLS traffic on them . My core routers are running EIGRP now. Please advice ! Thanks !

1 Accepted Solution

Accepted Solutions

I will rather say that the load sharing is like you have it in CEF. And your EIGRP routes will determine your MPLS forwarding table.

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7 Replies 7

Harold Ritter
Cisco Employee
Cisco Employee

MPLS loadsharing is indeed possible. If the packets being carried on top of MPLS are IPv4 then the hashing algorithm, to select the outbound interface, is based on the IPv4 source and destination addresses.

Otherwise, the inner label (bottom of stack) is used by the hashing algorithm to determine the outbound interface.

Hope this helps,

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

Hello,

Thanks you for your reply !

As I get from your msg , for my scenario , when enable MPLS ip on all 3 pairs of interface (3 links between 2 P routers) . The MPLS loadsharing is then like that of a etherchannel , am I wrong ? and does my EIRGP routing have any effect on packet forwarding interface selection ?

I will rather say that the load sharing is like you have it in CEF. And your EIGRP routes will determine your MPLS forwarding table.

Hi Olorunloba,

Thank you for your help !

Regards,

Hi, just for clarification, what Harold wrote is the hashing algorithm used with CEF forwarding of labeled packets. Per default it is (IP) destination based. If there is no IPv4 header detectable (f.e. EoMPLS), then the bottom label is used by CEF to forward labeled packets.

All this is done to avoid packet reordering problems.

Path selection in the MPLS core is based on your IGP, this is, what olorunloba wrote. For PE to PE traffic in most cases IGP paths to BGP next-hop addresses are used for load sharing across different pathes.

So both answers above contain part of the whole picture.

Hope this helps! Please rate all posts.

Regards, Martin

Just as a clarification, CEF is still ultimately responsible for the loadsharing, whether it is for IPv4 or MPLS.

Hope this helps,

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

Hi Martin & Harold,

Thank you both for your clarifications . It's very clear now . I much appreciate your helps .

Once again thank you !

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