Junos Asymmetric Routing

Ricardo Tavares curupas at gmail.com
Fri May 28 01:21:05 UTC 2010

f the route announce is coming from the BGP neighbor you need to
verify if the next-hop indicated for this route is itself reached by
the router, if by recursion the router do not resolve how to go to the
next-hop then the announced route will be not available. THe bgp
sender must set the next-hop with a reachable address, sometimes this
is achieved by the sender using the next-hop-self in the export
policy, but it is possible other situations where the next-hop is

If the sender is using a specific address for all the next-hops for
all the announced routes you will need just a static route pointing to the
gateway for his next-hop. If the BGP session for some reasons goes
down then the default route will apply and the redundancy through ISP1
will work fine.

Best Regards,

On Thu, May 27, 2010 at 9:38 PM, Ken Gilmour <ken.gilmour at gmail.com> wrote:
> Wow, very fast responses, Thanks Larry Sheldon and Ricardo Tavares!
> On 27 May 2010 18:07, Ricardo Tavares <curupas at gmail.com> wrote:
>> Not sure if I correctly undestand you but default route its the route
>> that the packet must follow if it do not have a specific route for the
>> destination, so, if the next-hop for the source IP ( is not in
>> the route table then the packet will follow the default route (ISP1).
> Yes I believe that would be the default if the session was initiated on the
> inside, but if it comes from outside on a particular interface which is not
> the default route, why would the router then send the packet out another
> interface? Should the device not route session-based traffic according to
> where it originated?
>> So, this behavior will be correct if next-hop for is not
>> installed. Just for troubleshooting purpose install a static route
>> like:
>> set routing-options static route next-hop
>> <the-correct-gateway-address> (ISP2)
> Yes sir, this works, but when you change the static route to point
> to the next hop on the virtual router for the particular interface (ISP2) it
> starts going over the interface for ISP1 again. I also set
> qualified-next-hop for ISP2 in the main routing table to no avail.
>> If this works fine then verify the route table, are you using BGP to
>> receive such routing info? If you are not filtering the update maybe
>> the sender is. Verify the received routes using the "show route
>> protocol bgp receive-protocol bgp x.x.x.x" (x.x.x.x is the bgp
>> neighbor)
> Yes sir, I have also gone to the extent of deactivating BGP and using only
> static routes.
> Thanks for your help!
> Regards,
> Ken

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