For OSPF, if no loopback address is configured OSPF
uses the highest IP address on the router being used.
This could be a WAN interface. You may be running OSPF
only on your Ethernet interface and not this WAN
interface OSPF is using for the router ID.
If the WAN interface bounces, it effects OSPF and
causes OSPF to re-converge. If you have a loopback
interface, then OSPF will use the highest IP on a
loopback as it's router ID and thus when the WAN
interface bounces it's not going to effect the OSPF
process.
--- suaveguru <[EMAIL PROTECTED]> wrote:
> if I am not wrong for some routing protocols like
> ospf
> it needs a always up interface like a loopback
> interface . Also for BGP peering with a loopback
> interface makes tcp connection more reliable
>
>
> suaveguru
> --- whitaker <[EMAIL PROTECTED]> wrote:
> > Could someone explain the importance of using
> > loopback interfaces? I keep
> > reading that it is important when using routing
> > protocols to use loopback
> > interfaces. A consultant that is writing
> > documentation for me suggested I
> > obtain an entire class C network just for loopback
> > addresses. Cisco says
> > when configuring BGP that, "We recommend you use a
> > loopback interface to
> > guarantee reachability in networks with multiple
> > paths." (from
> > http://www.cisco.com/warp/public/459/23.html#3).
> >
> > Maybe I'm missing something totally obvious here,
> > but exactly what benefit
> > do I gain from using loopback addresses? I know
> it
> > is supposed to provide
> > reliability for routing protocols, but how?
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