From: Brian Dennis (brian@5g.net)
Date: Fri Sep 13 2002 - 02:47:49 GMT-3
A standard serial interface is point-to-point so no mapping is needed. A
router assumes that all layer 3 addresses are at the other end of the
link, even its own IP address. That's why when you ping yourself on a
standard serial interface it takes twice as long for the reply then when
you ping the remote end.
Try this with two routers back-to-back:
<R1_Config>
int s0
ip add 1.1.1.1 255.255.255.0
clock rate 64000
no shut
</R1_Config>
<R2_Config>
int s0
ip add 1.1.1.1 255.255.255.0
no shut
</R2_Config>
Now from R1 when you telnet to 1.1.1.1 where do you end up?
Lastly since loopbacks are software-based (virtual) there isn't a layer
2 protocol associated with them and in turn no need for a mappings.
Brian Dennis, CCIE #2210 (R&S/ISP Dial)
-----Original Message-----
From: Volkov, Dmitry (Toronto - BCE) [mailto:dmitry_volkov@ca.ml.com]
Sent: Thursday, September 12, 2002 10:15 PM
To: 'Brian Dennis'
Cc: Ciscomonkey@aol.com; ccielab@groupstudy.com
Subject: RE: ISDN question
Brian,
Where is (how to see) L3 to L2 mapping for Loopbacks or serial
interfaces ?
Thanks,
Dmitry
> -----Original Message-----
> From: Brian Dennis [mailto:brian@5g.net]
> Sent: Friday, September 13, 2002 12:42 AM
> To: Ciscomonkey@aol.com; BIGB97750@aol.com; ccielab@groupstudy.com
> Subject: RE: ISDN question
>
>
> Correct. With Ethernet the router has a layer 3 to layer 2 mapping so
> there isn't an issue.
>
> Chief_Wiggum>sho arp
> Protocol Address Age (min) Hardware Addr Type Interface
> Internet 172.16.1.1 - 0001.9663.96c1 ARPA
> Ethernet0/1
> Chief_Wiggum>
>
> Brian Dennis, CCIE #2210 (R&S/ISP Dial)
>
> -----Original Message-----
> From: Ciscomonkey@aol.com [mailto:Ciscomonkey@aol.com]
> Sent: Thursday, September 12, 2002 9:18 PM
> To: brian@5g.net; BIGB97750@aol.com; ccielab@groupstudy.com
> Subject: Re: ISDN question
>
> He probably is comparing it to his ethernet interface whereas he can
> ping the
> ethernet interface once it has an IP address and is in the NO SHUT
> state, but
> can't do the same with the BRI interface. Is that correct?
>
> JJ
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