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Subject: Re: IP unnumbered [7:18250]
Dave,
I agree totally with your statement, however, I don't understand why you say
that if you use ip unnumbered pointing to a LoopBack interface that
nullifies the point of using unnumbered (to save IPs). You can still use a
single IP address on a LoopBack
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Subject: Re: IP unnumbered [7:18250]
Dave,
I agree totally with your statement, however, I don't understand why you
say
that if you use ip unnumbered pointing to a LoopBack interface that
nullifies the point of using unnumbered (to save IPs). You can still use a
single IP address on a LoopBack
Hi
Instead of using a numbered link you can use ip unnumbered to connect
sites.
Example:
Router A:
interface fastethernet 0
ip address 10.100.2.1 255.255.255.0
interface serial 0
ip unnumbered fasthethernet 0
Router B:
interface fastethernet 0
ip address 10.100.31 255.255.255.0
Brett gives a good example that will work just fine but I would not
recommend using IP unnumbered. With RFC 1918 you have more IP addesses
than your going to need so no problems with using registered addresses
on p-to-p links. troubleshooting also becomes trickier but if you
insist on using
Dave,
I agree totally with your statement, however, I don't understand why you say
that if you use ip unnumbered pointing to a LoopBack interface that
nullifies the point of using unnumbered (to save IPs). You can still use a
single IP address on a LoopBack not waste more by putting separate
At this point, it think it would be good to mention that (IMHO) it's best to
use the LoopBack interface for ip unnumbered because it can never go
down..
In the config snipet you gave, your Serial0 couldn't communicate if
FastEthernet0 went down.
I do believe that with some version of 12.x,
Agree, you don't use as many address with LB's as p-to-p networks but
the primary point I was trying to make before I rambled is that there is
really no good reason IMHO to ip unnumbered.
Dave
Michael L. Williams wrote:
Dave,
I agree totally with your statement, however, I don't
Sure, IP unnumbered is frequently used by ISP's to save address space and
for ease of configuration. Lets say you have a 7513 with 280 T1 customers
on it, that would mean wasting 280 /30 IP blocks just on interface transit,
so why use those IP's if you don't have a specific reason to? That is
When IP addresses are hard to come by (remember: a /30 subnet takes 4
addresses). When you don't want to deal with administering tons of /30
subnets that would comprise the WAN links.
There are probably other reasons. These were the first to come to mind.
Ken Diliberto
CCNA, CCNP, Ericsson E1
you might use it if you had say an access-server
e.g you got group-async 1 and group-async
the router wont let you do 'ip address 10.0.0.1 255.0.0.0 on both interfaces
so instead you would assign 10.0.0.1 to loopback 0
and then in group-async 1 2
ip unnumbered loopback 0
thus giving them both
Another advantage of IP unumbered, is if you have say 250 T1 customers
hanging off a router, and you default router them out there serial
interface:
ip route 0.0.0.0 0.0.0.0 s0
then, if you ever want to move customers to another router, you don't have
to have access to there router to do
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