2013年8月14日星期三

BGP Load Balancing Scenario

Question:

I am looking WS-C3560X-48PF-L  for some guidance with the following. I have a feeling I am missing something or that there is a better way

I have the following setup, eBGP to the same ISP, iBGP inside the AS between the routers and 6509s

I would like to do the following, lets say I have 1.1.1.0.... 1.1.6.0

These are advertised by my 6509s through BGP. I would like to balance the traffic across both of the links, so inbound/outbound traffic would be

1.1.1.0 to 3925 (primary) and 3825 as secondary
1.1.2.0 to 3825 (primary) and 3925 as secondary

I was thinking I should be able to do this using route maps

on the 3925

access-list 1 permit 1.1.1.0
access-list 1 permit 1.1.3.0
access-list 1 permit 1.1.5.0
access-list 2 permit 1.1.2.0
access-list 2 permit 1.1.4.0
access-list 2 permit 1.1.6.0

route-map subnet permit 10
match ip address 1
set as-path prepend 65401 65401

route-map subnet permit 20
match ip address 2

router bgp x.x.x.x
neighbor <core1> route-map subnet in
neighbor <core2> route-map subnet in

3825
access-list 1 permit 1.1.1.0
access-list 1 permit 1.1.3.0
access-list 1 permit 1.1.5.0
access-list 2 permit 1.1.2.0
access-list 2 permit 1.1.4.0
access-list 2 permit 1.1.6.0

route-map subnet permit 10
match ip address 2
set as-path prepend 65401 65401

route-map subnet permit 20
match ip address 1

router bgp x.x.x.x
neighbor <core1> route-map subnet in
neighbor <core2> route-map subnet in

Any help would be much appreciated

Answer:

if you are doing eBGP to the same AS ISP you can use MED outbound to influence how traffic is routed to your network and so setting a lower or higher metric is enough.

In any case the route-map should be applied outbound to the eBGP neighbor and not inbound to the iBGP sessions.
This is the usual practice.

route-map toISP-NA permit 10
match ip address 1
set metric 1000
route-map toISP-NA permit 20
match ip address 2
set metric 500

router bgp x.x.x.x
neigh <e-bgp-neigh> route-map toISP-NA out

on second border router

route-map toISP-NB permit 10
match ip address 1
set metric 500
route-map toISP-NB permit 20
match ip address 2
set metric 1000

router bgp x.x.x.x

neigh <e-bgp-neigh> route-map toISP-NB out

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