From: Edison Ortiz (edisonmortiz@gmail.com)
Date: Sun Jul 06 2008 - 17:00:48 ART
Additionally, 'ip unnumbered'?
Let's consider assigning IP addresses to the interfaces of a router using a
class B network that has been subnetted using eight bits of subnetting.
Every interface requires a unique subnet. Although each point-to-point
serial connection has only two end points to address, if we assign an entire
subnet to each serial interface, we use 254 available addresses for each
interface where only two addresses are needed. If we use IP unnumbered on
each serial interface, we save address space; the address of a LAN interface
is "borrowed" and used as the source address for routing updates and packets
sourced from the serial interface. In this way, address space is conserved.
IP unnumbered only makes sense for point-to-point links.
A router receiving a routing update installs the source address of the
update as the next hop in its routing table. Normally, the next hop is a
directly-connected network node. This is no longer the case if we use IP
unnumbered because each serial interface "borrows" their IP address from a
different LAN interface, each in a different subnet and possibly in a
different major network. When IP unnumbered is configured, routes learned
through the IP unnumbered interface have the interface as the next hop
instead of the source address of the routing update. Thus we avoid an
invalid next hop address problem due to the source of the routing update
coming from a next hop that is not directly connected.
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080
094e8d.shtml#ip_ip_un
Edison Ortiz
Routing and Switching, CCIE # 17943
-----Original Message-----
From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
Fahad Khan
Sent: Sunday, July 06, 2008 3:45 PM
To: Sadiq Yakasai
Cc: Joseph Saad; Cisco certification
Subject: Re: IP address on serial interfaces of a router
What is the logic behined that I can assign 10.0.0.1/24 (exactly the same ip
address) on two serial interfaces of a single router???
R1#sh run
---output omitted---
interface Serial1/0
ip address 10.0.0.1 255.0.0.0
serial restart-delay 0
!
interface Serial1/1
ip address 10.0.0.1 255.0.0.0
serial restart-delay 0
Wont the router be confused when it will forward traffic for
10.0.0.0/24network??
Thanks and regards,
On 7/6/08, Sadiq Yakasai <sadiqtanko@gmail.com> wrote:
>
> Huh????
>
> And how is this exactly related to ethernet again? :-)
>
> We digress again!
>
>
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--Fahad Khan
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