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movingbits
Posts: 3
Registered: ‎03-07-2011
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Accepted Solution

Ex4200 / Junos source based bgp route preference

Hi guys,

 

 

I was wondering if anyone could point me in the right direction.

 

I have two links coming into my switch, both advertising the same set of routes via bgp.

I've also been assigned two subnets, 192.168.1.0/24 and 192.168.2.0/24 to expose to my servers, and two seperate subnets to do my bgp peering, for example purposes lets make that 172.16.1.0/24 and 172.16.2.0/24 respectively.

 

My switch has ips 192.168.1.1, 192.168.2.1, 172.16.1.1 and 172.16.2.1

My peers are 172.16.1.2 and 172.16.2.2

I advertise 192.168.1.0/24 to 172.16.1.2 and 192.16.2.0/24 to 172.16.2.2

 

Alright, the problem is that hosts originating in the 192.168.1.0/24 subnet must take routes advertised via 172.16.1.2 and hosts originating in 192.168.2.0/24 must take paths advertised by 172.16.2.2. There are acls on the remote side which prevent both subnets from being routeable via both paths. Right now I have one routing table with local preference one way or the other, but then I lose the active/active nature of this connection.

 

What is the preferred way to solve this? Should I use routing instances and set up separate routing domains? Is there an easy way to use policy routing to make a source range take a less preferred route? In the default scenario one path or the other ultimately gets preference and half of my hosts become unroutable.

 

Any advice would be much appreciated!

 

 

Thanks,

 

movingbits.

Distinguished Expert
aarseniev
Posts: 1,724
Registered: ‎08-21-2009
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Re: Ex4200 / Junos source based bgp route preference

 


movingbits wrote:

 

Alright, the problem is that hosts originating in the 192.168.1.0/24 subnet must take routes advertised via 172.16.1.2 and hosts originating in 192.168.2.0/24 must take paths advertised by 172.16.2.2. There are acls on the remote side which prevent both subnets from being routeable via both paths. Right now I have one routing table with local preference one way or the other, but then I lose the active/active nature of this connection.

 

What is the preferred way to solve this? Should I use routing instances and set up separate routing domains?

 

 


 

Hello,

If 192.168.1.0/24 never ever has to talk to 172.16.2.2 and 192.168.2.0/24 never ever has to talk to 172.16.1.2 then I'd suggest 2 virtual-routers and 2 BGP sessions with management & access via global table/inet.0.

If you are looking for some kind of failover, like 192.168.1.0/24 normally talks to 172.16.1.2 and only talks to 172.16.2.2 when 172.16.1.2 is unavailable (and similarly for 192.16.2.0/24) then forwarding-instances with carefully constructed import policies and FW filters is the way to go.

HTH

Rgds

Alex

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Visitor
movingbits
Posts: 3
Registered: ‎03-07-2011
0

Re: Ex4200 / Junos source based bgp route preference

This is pretty much what I thought. I'll try to get that working and report back, thanks for the tip!

 

Ideally failover would be possible, but because of ACL's on the far side its not actually possible, its got to be active / active.

 

 

 

Thanks again.

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