dear,
i understand why i need multihop=2 for 2 routers case. however this
logic does not apply when i have 3 routers, where BGP can still be up
for multihop=2. shouldn't no. of hops = 3?
chris
Stephen Gill wrote:
>
> Consider the loopback as being routed, thus the ttl is decremented
> since they are not on the same network. IE. Source IP of the packet
> shows up as the loopback IP, not the directly connected interface, and
> Dest IP of the packet shows up as the remote loopback IP, not the
> directly connected interface.
>
> -- steve
>
> --- chris <chris@chrisland.net> wrote:
> > yup. but it can't explain the case when 2 routers are connected
> > back-to-back but "ebgp-multihop 2 (or larger)" is still necessary to
> > bring up BGP with loopbacks.
> >
> > chris
> >
> > Stephen Gill wrote:
> > >
> > > I believe this directly corelates to the TTL set in the packet. It
> > is
> > > counted just like the TTL would be when routing packets. IE,
> > decrement
> > > the TTL by one at every hop.
> > >
> > > -- steve
> > >
> > > --- chris <chris@chrisland.net> wrote:
> > > > Dear all,
> > > >
> > > > When I have 2 routers connected back-to-back and eBGP peered with
> > > > their
> > > > loopbacks, eBGP can only be up with eBGP-multihop >= 2. However,
> > > > when
> > > > these 2 routers are connected via another router, eBGP can still
> > be
> > > > up.
> > > > E.g.:
> > > >
> > > > Router A <--- eth ---> Router X <--- eth ---> Router B
> > > >
> > > > eBGP between A and B's loopbacks can be up with eBGP-multihop =
> > 2.
> > > >
> > > > Isn't it "3"? How is it calculated?
> > > >
> > > > Thanks.
> > > >
> > > > Regards,
> > > > Chris
> > > >
> > >
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