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May sound like a stupid question but just wanted to make sure. Does every serial connection need to have its own IP address.

Router 1:
Serial 0/0/0 IP address
Serial 0/1/0 IP address

Router 2:
Serial 0/0/0 IP address

Router 3:
Serial 0/1/0 IP address
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Every interface that expects to route IP generally needs an IP address. –  Joseph Kern May 7 '12 at 0:06

2 Answers 2

up vote 4 down vote accepted

No. A point-to-point link does not have to have its own IP address. Point-to-point links can be unnumbered.

You can, for example, have one router with an IP address of on the LAN and another router with an IP address of on the LAN. They can have a serial link with one end numbered and the other without needing additional IP addresses just for the link.

Logically, to enable IP on interface S0, you would need to configure a unique IP address on it. However, it is also possible to enable IP on the Serial interface and bring it up without assigning a unique IP address to it. This is done by borrowing an IP address already configured on one of the router's other interfaces. To do this, the ip unnumbered interface mode command is used as shown below. -- Understanding and Configuring the ip unnumbered Command

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Just to corroborate: I have run many Serial point-to-point connections passing IP that didn't have IP addresses. –  wfaulk May 7 '12 at 0:33

Every interface on an IP router needs its own IP address, yes.

However, if you're using IPv6 the cool thing is that it can be the same IPv6 address (link-local address).

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ok just in our spec we have been given the ip on the serial connection from the isp router to isp and the internet gateway address, got my network working just not sure how to connect it all up to the isp –  Melevin Mandana May 6 '12 at 19:34
This is just false. Point-to-point links do not need their own IP address. –  David Schwartz May 6 '12 at 23:41
… I learned something! –  MikeyB May 7 '12 at 13:46

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