Junos Asymmetric Routing

Larry Sheldon LarrySheldon at cox.net
Thu May 27 20:49:06 CDT 2010


On 5/27/2010 19:38, Ken Gilmour 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 (3.3.3.3) 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?

I'm close to the edge of what I know (or remember--i've been inactive
for a while) but when a packet arrives on an interface, the routing
engine has to decide where to poke it bqased on what is in the
packet--there is no information as to where it came from, or to what it
is a response.  If it isn't in the IP header, it isn't available for
routing decisions.  ("Policy routing" can provide additional data, as
can source routing.  But one requires a human being to provide the rule,
and the other requires somebody or something else outside the router to
calculate the route.  I don't think anybody much allows source routing
anymore.)


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