From: Fahad Khan (fahad.khan@gmail.com)
Date: Mon Jul 07 2008 - 07:44:43 ART
Ok thanks I understand. But in case of bundling (MLPPP) we put the IP
address on multilink interafce, not on the individual interafces i think.
kindly shed light on unidirectional link scenario as well.
thanks alot.
On Mon, Jul 7, 2008 at 3:16 AM, Carlos G Mendioroz <tron@huapi.ba.ar> wrote:
> The BUG seems to be in the design.
> That the router lets you put some configuration that in this case
> leads to a non operative implementation is a consequence of flexibility.
> Having the same IP in more than one interface is useful on some situations,
> some have been mentioned already (bundling), there are others (e.g.
> unidirectional links).
>
> So answering your question (two different semantics):
>
> Q1: Why does it let you put the same address ?
> A1: Beacuse sometimes it's needed
>
> Q2: Why not on ethernets ?
> A2: Because someone at cisco does not think A1 holds here...
>
> -Carlos
>
> Fahad Khan @ 07/07/2008 05:25 -0300 dixit:
>
>> here is the scenario
>> R1(s1/0 - 10.0.0.1/8) ---------------(s1/0-10.0.0.2/8) R2
>> R1(s1/1 - 10.0.0.1/8) ---------------(s1/0-10.0.0.3/8) R3
>>
>> R1# sh ip route
>>
>> C 10.0.0.0/8 is directly connected, Serial1/0
>> is directly connected, Serial1/1
>>
>>
>> -when R2 pings to R1(10.0.0.1), its fine, but
>>
>> -when R3 pings to R1(10.0.0.1), it wont get reply since the "debug ip
>> packet" on R1 shows that R1 goes to reply R3 from its serial1/0 interface
>> where R2 is connected, "debug ip packet" on R2 shows that R2 is getting
>> reply .
>>
>>
>> is this a bug? now router is confused to send traffic....
>>
>> Dear Roman,
>>
>> Kindly tell me the logic in case of Frame-relay subinterfaces..?
>>
>>
>> On Sun, Jul 6, 2008 at 5:40 PM, Jason Madsen <madsen.jason@gmail.com>
>> wrote:
>>
>> BVIs seem to work just fine too.
>>>
>>> Jason
>>>
>>>
>>> On Sun, Jul 6, 2008 at 2:00 PM, Edison Ortiz <edisonmortiz@gmail.com>
>>> wrote:
>>>
>>> Additionally, 'ip unnumbered'?
>>>>
>>>>
>>>>
>>>> Let's consider assigning IP addresses to the interfaces of a router
>>>> using
>>>> a
>>>> class B network that has been subnetted using eight bits of subnetting.
>>>> Every interface requires a unique subnet. Although each point-to-point
>>>> serial connection has only two end points to address, if we assign an
>>>> entire
>>>> subnet to each serial interface, we use 254 available addresses for each
>>>> interface where only two addresses are needed. If we use IP unnumbered
>>>> on
>>>> each serial interface, we save address space; the address of a LAN
>>>> interface
>>>> is "borrowed" and used as the source address for routing updates and
>>>> packets
>>>> sourced from the serial interface. In this way, address space is
>>>> conserved.
>>>> IP unnumbered only makes sense for point-to-point links.
>>>>
>>>> A router receiving a routing update installs the source address of the
>>>> update as the next hop in its routing table. Normally, the next hop is a
>>>> directly-connected network node. This is no longer the case if we use IP
>>>> unnumbered because each serial interface "borrows" their IP address from
>>>> a
>>>> different LAN interface, each in a different subnet and possibly in a
>>>> different major network. When IP unnumbered is configured, routes
>>>> learned
>>>> through the IP unnumbered interface have the interface as the next hop
>>>> instead of the source address of the routing update. Thus we avoid an
>>>> invalid next hop address problem due to the source of the routing update
>>>> coming from a next hop that is not directly connected.
>>>>
>>>>
>>>>
>>>> http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080
>>>> 094e8d.shtml#ip_ip_un<
>>>> http://www.cisco.com/en/US/tech/tk648/tk362/technologies_tech_note09186a0080094e8d.shtml#ip_ip_un
>>>> >
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Edison Ortiz
>>>>
>>>> Routing and Switching, CCIE # 17943
>>>>
>>>>
>>>>
>>>> -----Original Message-----
>>>> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf Of
>>>> Fahad Khan
>>>> Sent: Sunday, July 06, 2008 3:45 PM
>>>> To: Sadiq Yakasai
>>>> Cc: Joseph Saad; Cisco certification
>>>> Subject: Re: IP address on serial interfaces of a router
>>>>
>>>>
>>>>
>>>> What is the logic behined that I can assign 10.0.0.1/24 (exactly the
>>>> same
>>>> ip
>>>>
>>>> address) on two serial interfaces of a single router???
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> R1#sh run
>>>>
>>>>
>>>>
>>>> ---output omitted---
>>>>
>>>>
>>>>
>>>> interface Serial1/0
>>>>
>>>> ip address 10.0.0.1 255.0.0.0
>>>>
>>>> serial restart-delay 0
>>>>
>>>> !
>>>>
>>>> interface Serial1/1
>>>>
>>>> ip address 10.0.0.1 255.0.0.0
>>>>
>>>> serial restart-delay 0
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> Wont the router be confused when it will forward traffic for
>>>>
>>>> 10.0.0.0/24network??
>>>>
>>>>
>>>>
>>>> Thanks and regards,
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> On 7/6/08, Sadiq Yakasai <sadiqtanko@gmail.com> wrote:
>>>>
>>>> Huh????
>>>>> And how is this exactly related to ethernet again? :-)
>>>>> We digress again!
>>>>> _______________________________________________________________________
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>>>>
>>>>
>>>>
>>>>
>>>> --
>>>>
>>>> Fahad Khan
>>>>
>>>>
>>>>
>>>>
>>>>
>>>> _______________________________________________________________________
>>>>
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>>>>
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>>>>
>>>>
>>>> _______________________________________________________________________
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>>>>
>>>>
>>>>
>>>>
>>>>
>>>>
>>
>>
> --
> Carlos G Mendioroz <tron@huapi.ba.ar> LW7 EQI Argentina
>
-- FAHAD KHAN
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