I can simply use the quote from Michael Williams' message above to answer
your question...
1. "A loopback is a logical interface that never goes down. It's used for
various reasons (for setting up various kinds of tunnels, for setting who is
the DR/BDR in OSPF, etc)."
2. "Many people use the subnet mask 255.255.255.255 because
that's the only way to assign a single IP to the lookback instead of using
more than 1 IP address." Therefore, you normally won't see /24s on loopback
interfaces.
Richard
""Sim, CT (Chee Tong)"" wrote in message
[EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> I have seems some routers with many lookback interfaces configured. May I
> know what is the purpose to have so many lookback? I thought one loopback
> can help us to troubleshoot the connectivity
>
> Besides, I am interested about question 5 from Richard, you said the
> lookback IPs within same network can be configured on different router.
> Does it mean that if we configured many lookback interfaces, those IPs
must
> be in different network. for example 192.168.101.101/24
192.168.102.102/24.
> But Any one know what is the reason??
>
>
> > 5) If I configured A's loopback IP to be 192.168.0.1/24, can we still
> > configured B's loopback to be 192.168.0.2/24? Note: there are in same
> > network.
> Sure you can since they are in two different routers. I won't recommend
> doing this though...
>
> The point is, there is no magic behind a loopback interface as you still
> need physical interface and routing entries if you need access.
>
> Richard
>
> -----Original Message-----
> From: Richard Chang [mailto:[EMAIL PROTECTED]]
> Sent: Thursday, June 28, 2001 1:51 AM
> To: [EMAIL PROTECTED]
> Subject: Re: what is loopback interface for ? [7:9493]
>
>
> See lines below.
>
>
> ""Susan Stone"" wrote in message
> [EMAIL PROTECTED]">news:[EMAIL PROTECTED]...
> > Hi..
> >
> > Sorry, I need a few more questions to verify whether my understanding on
> > loopback is correct or not? Pls answer it.
> >
> > 1) If I have two router A (loopback=192.168.0.1/32) and B
> > (loopback192.168.0.2/32), Router A's S1 int 100.100.100.1/24 is
connected
> to
> > Router B's S1 100.100.100.2/24. There are no more other connection. If
S1
> > of B is down. Can I still telnet from A to B using B's loopback
address.
> No.
> >
> > 2) If Router A and B have another connection. Router A's S2 int
> > 100.200.100.1/24 is connected to Router B's S2 100.200.100.2/24. If S1
of
> B
> > is down. Can I still telnet from A to B using B's loopback address?
> Yes, if you have correct routing entries.
> >
> > 3) If Router A doesn't have loopback int configured. Can we still
telnet
> > from A to B?
> Of course you can simply telnet into any physical interface that's still
up.
>
> >
> > 4) Whether the loopback IP address need to be in order or same network?
> Let
> > say Router A's loopback is 192.168.0.1/32 and Router B's loopback is
> > 20.20.20.1/8. Can we still telnet from A to B?
>
> Again, yes, if you have correct routing entries.
> >
> > 5) If I configured A's loopback IP to be 192.168.0.1/24, can we still
> > configured B's loopback to be 192.168.0.2/24? Note: there are in same
> > network.
> Sure you can since they are in two different routers. I won't recommend
> doing this though...
>
> The point is, there is no magic behind a loopback interface as you still
> need physical interface and routing entries if you need access.
>
> Richard
>
> >
> >
> >
> >
> >
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