On Wed, 19 Jul 2000, Niraj Palikhey wrote:
> Hi,
> I am trying to understand why a serial connection (s0) is not assigned an ip
> address to connect with the service provider when configured for frame
> relay.
Because you don't need to assign a PtP link its own IP address. The
traffic can really only go one place..........the other end of the pipe.
IP Unnumbered can be use.
> As a configuration example that one of my friends showed me, his serial 0 is
> configured for T1, with no ip address, serial 0.2 is configured for frame
> relay as a point-to-point subinterface. There is an ip unnumbered
Yes. When you do subinterfaces, you don't have to have an ip address or
even ip unnumbered on the physical interface. You can think of that sort
of like an Extended hard drive partition, and the subinterfaces are
logicals within the extended (now is that a bad analogy or what!?)
Some people don't like to use the physical interface........like
s0/0...........they prefer to just use the subinterfaces s0/0.1,
s0/0.2......and leave the physical interface just out there.
> Ethernet0/0 command for this interface and also the frame relay
> configuration is set (dlci #, lmi type etc)
> What does this ip unnumbered do in this case?
IP unnumbered tells the serial interface to use the ip of the interface
you specify. Its very common to use ip unnumbered to an ethernet
interface.......for example. If you have a router with a single ethernet
and a single serial PtP link. You can just use ip unnumbered. Alot of
"consumer" ISDN routers work this way........you don't number the serial
WAN interface and the ethernet LAN interface, you just assign the router
one ip number and thats used on all interfaces.
This IMHO, is good for stubs who are routed a subnet and thats not going
to change. I personally prefer to use numbered interfaces, because you
must use numbered interfaces if using a Routing protocol such as OSPF.
Sometimes people make the argument that they don't have the necessary ip
numbers to make /30's for the PtP links. You can use RFC 1918 speace,
with no translation needed, so long as its on your side of the border
router. This could break MTU Path Discovery, but you just have to ask
yourself what your needs are.
> Pg. 417 and 418 of the ICRC book from Cisco Press for CCNA 640-407 does not
> explain why the physical interface serial 2 and sub-interface serial 2.2
> point-to-point is not configured with any ip address NOR does it explain the
> use of the ip unnumbered Serial1(in this case).
> In this scenario, how does this router talk to the service provider's
> router?
> Does it just look at the DLCI number and use the virtual circuit for
> communication to the outside? What is involved?
> Please advise.
> Thank you.
> Kind regards,
> [EMAIL PROTECTED]
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-----------------------------------------------------
Brian Feeny, CCNA [EMAIL PROTECTED]
318-222-2638 x 109 http://www.shreve.net/~signal
Network Administrator ShreveNet Inc. (ASN 11881)
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