Routing

TOPOLOGY:

0/0 route >>>>>>
rtr1:[AS#1] <ebgp>  rtr2:[AS#65001] <ebgp>  rtr3:[AS#65002] <ebgp> rtr4:[AS#1]   


Scenario:
Default route is coming from rtr1:[AS#1]

On rtr2 it has to be passed along to rtr3 etc

Originally rtr2 was a Cisco device where simple "default-originate" command got rid of the rtr1 original AS#1 and all downstream routers saw that 0/0 is originating from rtr2AS#65001

Now by switching rtr2 to Juniper there are no direct alternative to that command. Working with policies I can't achieve same result. As it always exports active 0/0 from routing table it receives from rtr1, leaving AS#1 in the prefix path.
That causes an issue when 0/0 reaches rtr4:[AS#1], route is discarded as rtr4 sees own AS# in the AS_path and thinks theres a loop.

What might be feasible workarounds on rtr2 to get rtr4 accept that route?


The most simple way is to put "allowas-in"/ASloops# on rtr4, unfortunately its not under my control.
As-override also won't work on rtr2 as it doesn't peers directly with rtr4.

Quick and dirty solution would be to configure a static default route and point it at rtr1, then use policy export the default from 'protocol static' and deny the readvertisement of the BGP-learned route. 

Thanks evt,

As I’ve told that this is just a part of network.
I can’t overwrite BGP route with static, as rtr2 has two upstream bgp peers, receiving 0/0.

Manual "floating statics" /route tracking + redistributing to bgp is also on the list, but then redundant upstrem bgp looses its primary purpose and might be more complex to tshoot for junior staff and support.

This is an interesting topology and in my defense, the original post did not provide a lot of details.  Out of curiosity, why are you receiving a default route from AS1, then readvertising the default back to AS1?

My next suggestion would be to use a generated default route on rtr2, but you may need to tweak this for your environment.  I tested this in the lab and it works for the exact scenario you posted, but doesn't really take into account other routers in the as65001 network or the other ISP.

routing-options {
    generate {
        route 0.0.0.0/0 policy upstream-default;
    }
}
policy-options {
    policy-statement upstream-default {
        from {
            protocol bgp;
            as-path as1;
            route-filter 0.0.0.0/0 exact;
        }
        then accept;
    }
    as-path as1 "^1$";
}

Sorry for confusing, I didn't want to overwhelm with a bunch of unnecessary info and keep the original post short.
Will try your solution in the next maintenance window.

[quote]
Out of curiosity, why are you receiving a default route from AS1, then readvertising the default back to AS1?
[/quote]

Basically rtr1 and rtr4 both are the exact same physical ISP MPLS PE device, only  in different vrfs, thus having same AS#
On rtr1<>rtr2 exchange: rtr2 has public inet peering. and receives 0/0 to public inet.
On rtr2<>rtr3 exchange: this default route must be propogated to internal corporate WAN

Hopefully I managed to explain that clear enough.