From: Scott Morris (swm@emanon.com)
Date: Sun Feb 04 2007 - 02:32:53 ART
If you are talking about a packet coming in from one subnet going to
another, then yes there will still be routing. Again, looking to that debug
command, what you will see is that a RIB decision (routing information base)
is made, but a FIB lookup (forwarding information base) was perhaps unable
to come up with the correct information.
Routing will still take place, but according to your notes there, both
subnets are on the same physical interface, correct?
> C 173.12.23.0 connected to S0/0
> C 173.23.23.0 connected to S0/0
Beyond that... Remember that routing works both directions. So even though
your ping may may it TO the destination you want (since one router has a
default?), that receiving router may not have a clue how to get back...
Again, looking at the debug, perhaps on all routers, should indicate what's
happening.
HTH,
Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713, JNCIE
#153, CISSP, et al.
CCSI/JNCI-M/JNCI-J
IPexpert VP - Curriculum Development
IPexpert Sr. Technical Instructor
smorris@ipexpert.com
http://www.ipexpert.com
-----Original Message-----
From: Mohammad Saeed [mailto:mzsaeed@gmail.com]
Sent: Sunday, February 04, 2007 12:22 AM
To: swm@emanon.com
Cc: Cisco certification
Subject: Re: Very basic Routing Question!!!!
So, theoratically atleast, a router shall not need to perform routing
betweeb its directly connected networks? Am I right? Because it has all the
entries in the routing table with C (Directly Connected)!!!
And as per my understanding, this how routing process happens, that router
receives the frame, will remove ethernet header, look at the destnation
network address, go and check if he knows how to reach that network in its
routing table, find the entry for that network, prepare new ethernet frame
and send out that interface!!!!!
Regards,
Mohammad Zahed Saeed
On 2/3/07, Scott Morris <swm@emanon.com> wrote:
> The best thing to do here is "debug ip packet" and see what the router
> tells you. Most likely what you will be seeing there is an "encapsulation
failed"
> message, which means that something within your configuration is not
> allowing/not returning a Layer2 address for you.
>
> In ethernet world, we have arp that magically does the Layer3 -->
> Layer2 resolution for us. Depending on your configuration of serial
> lines (frame
> relay???) things may need to be manually set.
>
> In any event, the debug will help you get a handle on what the router
> is attempting to do there.
>
> HTH,
>
>
> Scott Morris, CCIE4 (R&S/ISP-Dial/Security/Service Provider) #4713,
> JNCIE #153, CISSP, et al.
> CCSI/JNCI-M/JNCI-J
> IPexpert VP - Curriculum Development
> IPexpert Sr. Technical Instructor
> smorris@ipexpert.com
> http://www.ipexpert.com
>
>
>
> -----Original Message-----
> From: nobody@groupstudy.com [mailto:nobody@groupstudy.com] On Behalf
> Of Mohammad Saeed
> Sent: Saturday, February 03, 2007 11:56 PM
> To: Cisco certification
> Subject: Very basic Routing Question!!!!
>
> Hi,
>
> Sorry, my last email I didn't complete and was sent by mistake....
>
> R1's S0/0 is connected to R5's S0/0.1 and they have network address
> 170.12.23.0/24 with IP Address 170.12.23.1 and 170.12.23.5.
>
> R5 has another S0/0.2 and have IP 173.23.23.5/24. On R1 you give
> default route
>
> ip route 0.0.0.0 0.0.0.0 serial 0/0
>
> Now as R5 has
>
> C 173.12.23.0 connected to S0/0
> C 173.23.23.0 connected to S0/0
>
> in the Routing table and R 1 has defalut route to R5, if you say
>
> R1# ping 173.23.23.5
>
> Why R5 does not respond, when it has the entry for 173.23.23.5 in the
> routing table and R1 is sending the packets with source IP 173.12.23.1????
> Because as I understand, R1 will send the packets for any destination
> to R5,
> R5 shall look in to its RT that destination is 173.23.23.0, do I know
> how to reach this network, Yes, it is directly connected, so it shall
> respond, but its not, can any bosy explain why?
>
> Regards,
>
> Mohammad Zahed
>
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