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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 172.10.80.193/30
Serial 0/1/0 IP address 172.10.80.197/30

Router 2:
Serial 0/0/0 IP address 172.10.80.194/30

Router 3:
Serial 0/1/0 IP address 172.10.80.198/30
MikeyB
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Melevin Mandana
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2 Answers2

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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 192.168.120.3 on the 192.168.120.0/24 LAN and another router with an IP address of 192.168.121.9 on the 192.168.121.0/24 LAN. They can have a serial link with one end numbered 192.168.120.3 and the other 192.168.121.9 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

David Schwartz
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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 07 '12 at 00:33
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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).

MikeyB
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