From: Brian McGahan (bmcgahan@internetworkexpert.com)
Date: Tue Jan 04 2005 - 16:20:57 GMT-3
Rick,
> This example is using loopbacks for all ibgp peering and interface
> addresses
> for ebgp(R1-R2) and R3 is a route reflector to R2 and R4:
> R1---ebgp----R2----ospf & ibgp-----R3-----ospf & ibgp------R4
>
> The link between R1 and R2 is not advertised in BGP, however R3 gets
the
> routes with R2's loopback as the next-hop. Now since R3 knows how to
get
> to
> the loopback it will install the route and advertise the learned
routes on
> to
> R4.
Did you test this? What you describe will only be the behavior if you
issued the "next-hop-self" command or manually modified the next-hop
with a route-map. Normal behavior is that R3 will see the next-hop as
the IP address of R1's interface connecting to R2.
HTH,
Brian McGahan, CCIE #8593
bmcgahan@internetworkexpert.com
Internetwork Expert, Inc.
http://www.InternetworkExpert.com
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> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
Of
> Rick
> Sent: Saturday, January 01, 2005 10:16 PM
> To: Cisco certification
> Subject: next hop self
>
> I have a question regarding next hop self. When you have a bgp peering
> session
> using loopbacks and updatesource lo0 the next hop of the advertised
> routes
> have the loopback address instead of the interface address. Here is a
> where my
> questions comes from
>
> This example is using interface addresses for all bgp peering and R3
is a
> route reflector to R2 and R4:
> R1---ebgp----R2----ospf & ibgp-----R3-----ospf & ibgp------R4
>
>
> The link between R1 and R2 is not advertised in BGP so when R3
receives
> the
> routes it will not install as it can't resolve the next hop. to solve
this
> problem you just use next-hop-self on R2 to R3 and then R3 will
install
> the
> routes and advertise them on to R4
>
>
> This example is using loopbacks for all ibgp peering and interface
> addresses
> for ebgp(R1-R2) and R3 is a route reflector to R2 and R4:
> R1---ebgp----R2----ospf & ibgp-----R3-----ospf & ibgp------R4
>
> The link between R1 and R2 is not advertised in BGP, however R3 gets
the
> routes with R2's loopback as the next-hop. Now since R3 knows how to
get
> to
> the loopback it will install the route and advertise the learned
routes on
> to
> R4.
>
>
> So my questions are should we still use next-hop-self with the second
> example
> even though it isn't needed? For lab purposes is there a reason to not
> peer
> with loopbacks unless of course you are instructed not to?
>
> Rick
>
>
This archive was generated by hypermail 2.1.4 : Wed Feb 02 2005 - 22:10:18 GMT-3