Outgoing BGP Updates - Same Links

[netbeginner]

Hi Experts,

Please suggest,  - How to influence Outgoing traffic/updates in BGP with two links from same service provider.

Rgds

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[Georg Pauwen]

Hello,

use weight and/or local preference:

https://keepingitclassless.net/2011/09/bgp-weight-and-local-preference/

[netbeginner]

Hi George, 

Remember in my case there are 02 ISPs and both are from same Service provider. hope you have consider 

[Georg Pauwen]

Hello,

the weight attribute is configured on a per neighbor basis, so even if you have two links with the same provider, it will still work.

As Paul asked, tell us if you are using one or multiple routers, and if there are multiple, how they are interconnected...

[netbeginner]

Hi George, 

Thanks..

Understand that highest weight will be preferred.

In my case , we have two routers. Link-1(ISP-A) is connected on Router-1 , Link-2(ISP-1) is connected on Router-2.

Both these routers are interconnected using a SWITCH from respective Routers LAN Interface configured with HSRP.

[Giuseppe Larosa]

Hello netbeginner,

if the routers are two you should use BGP local-preference (because BGP weight is local to a single router) and to configure an iBGP session between them.

The router setting the highest local preference will be the primary exit point and should also be the HSRP Active on internal LAN in normal conditions.

But if you want to use both links to the ISPs at the same time you can:

use two HSRP groups with different VIPs to be used as next hop addresses for static default routes on internal devices with R1 active for group1 and R2 active for group 2.

OR

Avoid to use HSRP and use a dynamic routing protocol like OSPF and have the border routers to inject a default route in OSPF if there is one in the BGP table/ IP routing table using

router ospf 10

default-information originate

Hope to help

Giuseppe

[netbeginner]

Pefect !!!! This is what i looking for. 

Just curious to know , What if we have single router at our end with same two links from same provider, guess in this case Weight will work.

[Giuseppe Larosa]

Hello,

if you had a single router you could use commands like

neighbor x.x.x.x weight 500

neighbor y.y.y.y weight 100

And this would work.

If you want to implement a primary link / hot standby secondary link use

R1

router bgp

neighbor x.x.x.x local-preference 500

R2

router bgp

neighbor y.y.y.y local-preference 150

100 is the default local preference value highest value is preferred.

Hope to help

Giuseppe

[netbeginner · Accepted solution]

Great !! 

Thanks Giuseppe

[paul driver]

Hello

You can use BGP path attributes weight or local preference to accommodate this however it does depend on how your topology is setup can you elaborate on this?

Are you using two bgp rtrs or just the one.

[netbeginner]

hi paul, 

scenario is simple only. but somehow confused as having both the WAN links from same provider (i.e. same AS).

[paul driver]

Hello

Having dual wan links to the same ISP isnt all that unusual but it does provide a possible resiliency issue is the isp runs into problems then you has a customer have a single point of failure to that ISP.

Can to confirm what it is you like to manipulate in-terms of your egress traffic towards the isp, if you are using a single wan rtr to peer with isp or dual rtrs.

Do you have the same ASN as the ISP or different

[netbeginner]

Hi Paul, 

02 links from same ISP with same AS. 

Suppose, I want to route all outgoing traffic from Link-1. We have dual router. 

For 02 WAN links on single router this is clear that we can use local pref or weight.

[paul driver]

Hello
Still not clear!

your site =  1 or 2 wan rtrs?
ISP = is their ASN the same as yours or is it different

[netbeginner]

Hi Paul, 

lemme try to clear again. 

We have two routers (RTR-A and RTR-B) at our end. Both these routers are connected with same service providers with 02 links i.e. one link on each router (Link-1 on Router-A and Link-2 on Router-B). 

Our End AS :  100

ISP End AS : 200 (same for both the links). 

Our end both routers are interconnected using switch from routers LAN interface (HSRP configured on the same).