The MPLS-OPS Archive

[Pegg Damon <Damon.Pegg@carrier1.com>]

The problem (I presume Cisco equipment) is that Cisco don't have a concept
of iBGP load-balancing unless this has been introduced in 12.2 code.  Within
iBGP, traffic can be balanced to the bgp-next-hop address based on
equal-cost IGP metrics but this is IGP balancing and not iBGP.  There is no
way to choose multiple BGP paths within iBGP from the same device and
experience has led me to bastardise natural routing with awkward route-maps
to achieve balancing in symetrical environments.  All other things being
equal, iBGP decision making is based on router-id, as you surmise.

With a single route-reflector, I suggest segregating routes received and
advertised using MEDs so that you achieve redundancy and prefix based
balancing.  In the event of a single prefix you may have to break it down to
mutliple longer prefixes, carried only internally, as well as potentially
advertising the customer's supernet externally.

A typical example for a multiple route-reflector environment...


---------P (RR)---------PE (RR Client)--------------CE 
           |
           |                 
---------P2(RR)---------PE2(RR Client)--------------CE2

...involves weight-based preference of routes received by the P from the PE
routers based on as_path regex prefix-list for those routes - i.e. P prefers
PE for routes from CE and P2 prefers PE2 for routes from CE2.  Of course P
will also connect physically to PE2; and P2 to PE; but this is not
represented above because these links won't be used by traffic for this
specific customer.  That takes care of outbound traffic and the customer can
take care of inbound by one of these methods (although I have had awkward
customers have me do use MEDs to handle the inbound traffic too.)

There really isn't a simple solution but believe me I have asked Cisco for
iBGP multipath support on several occasions :)

> -----Original Message-----
> From: Robertson, Kevin [mailto:Kevin.Robertson@Quantitude.com]
> Sent: 16 August 2001 14:50
> To: 'mpls-ops@mplsrc.com'
> Subject: Max-Paths & Max-Paths ibgp (MPLS BGP operation)
> 
> 
> I am looking for help to see how the Max-Paths/Max-Paths Ibgp 
> works within
> MPLS. I have a multi-homed enviroment and need to 
> load-balance to my final
> destination down 2 alternate links.
> 
> Help Needed.......
> 	I am running IBGP and EBGP in my environment, IBGP 
> between the Core
> multi-homed locations and EBGP down to the Destination host 
> CE's. I would
> like to know how the Max-Paths/Max-Paths IBGP affects the 
> other multi-homed
> routers in my environment without the need for 
> Load-Balancing.... (I sort of
> know how to get around that with route maps but unsure in the 
> MPLS world),
> However I am unable to get the Load-Balancing working and can 
> only get the
> traffic to go via best path determined by BGP. (Usually the 
> Highest Router
> ID)
> 
> Please note I have set the Med's down at the CE level for 
> equal cost paths,
> also running AS override and Route maps Set00 up at the PE routers. 
> 
> Any test configurations would be a bonus.
> 
> 			
> 		PE-------EBGP-------CE\
>  		|                              |   \
> R Reflec-----------	IBGP      	   IBGP	>destination host	
>  		|	                   |   /
> 		PE-------EBGP-------CE/
> 
> 
> 
> Regards, 
> 
> Kevin Robertson
> 
> Senior Network Engineer
> Network Planning & Engineering
> Quantitude Inc
> 5350 S. Valentia Way
> Englewood, CO 80111,USA
> Tel:  +001 720-535-2232 
> Efax: +001 503 907 8435
> Email:   Kevin.Robertson@quantitude.com 
> 
> 
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