why do we require a IP address for a Serial Port?

[anand]

My question might be silly, but i need to know, what is the purpose of having IP address on Serial Port, instead we can use the IP address of Ethernet Port by entering "ip unnumbered ethernet 0" on serial port isn't?

[Richard Burts]

I think a little historical perspective may help in answering this question. We tend to be so focused on the router as an IP protocol processor that we tend to forget that the router was developed as a multiprotocol processor (IP, IPX, Appletalk, Bridging, even protocols like XNS were supported at one time). As a multiprotocol processor no protocol is enabled on an interface by default. We must do something to activate or enable each protocol on the interface. We activate IP on the interface by assigning an IP address.

So if we want the serial interface to process IP we must assign an IP address to the interface. There is not a requirement that the address be unique (and no requirement that it must be in the same subnet as its neighbor on the other end of the serial link) and so we can use IP unnumbered on the serial interface. But without assigning some kind of IP address the interface would not process IP. That is the purpose of having an IP address on the serial port.

HTH

Rick

[amit-singh]

Rick its a great explanation. !!

Regards,

-amit singh

[ankurbhasin]

Hi,

One more bad outcome is there is we use "ip unnumbered" command.

We will not be able to manage it remotely and troubleshooting sometimes become very difficult.

That is also a reason we assign an ip address on serial interface.

Regards,

Ankur

[anand]

that was really gr8 in ur explanation

[jroyster]

Management and network management applications (as mentioned) are the "usual" answer.

The app will SNMP query each routers and get things like arp table, routing table, interface list, etc. With this information it can build a map of the network.