An old question, but one which I don't believe anyone answered. Speculative
question. Serves as a lesson in router behavior.
The question: can one, using ip unnumbered, configure several interfaces on
the same network?
Readers can read through the previous messages to get the idea of what was
discussed.
Answers:
1) Cisco permits ip unnumbered on point to point links only. This includes
frame relay subinterfaces that are configured point to point using the
interface x.y point-to-point command. One cannot configure an ethernet
interface as an ip unnumbered. Nor can one configure the loopback interface
as an ip unnumbered. ( IOS 12.1.1 IP Plus etc )
2) One can indeed have several interfaces configured as unnumbered using the
same source. Did so in the lab just now. Slap on the side of the head. I
once ran my company ( nine sites ) using ip unnumbered on all interfaces,
including frame relay subinterfaces. How quickly we forget. Brain arteries
must be hardening.
More complex question: can one then effectively have all associated
interfaces on one big network without explicitly having bridging enabled on
any of the connected interfaces?
In the course of this experiment, I configured two routers such that the
ethernet interfaces on each were addresses on the 172.16.0.0/16 network.
(172.16.1.1/16 on one and 172.16.2.2/16 on the other) I configured ip
unnumbered on both serial interfaces of each router, and connected those
interfaces to eachother. I.e. router 1 had two serial connections to router
2
Without a routing protocol configured, the sh ip route resulted in the
following:
Router_2#sh ip route
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.0.0/16 is directly connected, Ethernet0
C 172.16.1.1/32 is directly connected, Serial0
is directly connected, Serial1
C 192.168.1.0/24 is directly connected, Loopback0
Notice the directly connected serial interfaces, with the host route
172.16.1.1/32 showing over both s0 and s1
Now with OSP configured:
Gateway of last resort is not set
172.16.0.0/16 is variably subnetted, 2 subnets, 2 masks
C 172.16.0.0/16 is directly connected, Ethernet0
C 172.16.1.1/32 is directly connected, Serial0
is directly connected, Serial1
C 192.168.1.0/24 is directly connected, Loopback0
192.168.3.0/32 is subnetted, 1 subnets
O 192.168.3.1 [110/65] via 172.16.1.1, 00:00:03, Serial1
[110/65] via 172.16.1.1, 00:00:03, Serial0
notice that the ospf interface from the other router (192.168.3.1) appears.
No change in the serial interface routes. I should add that the
172.16.1.1/32 host route points to the ethernet interface of the other
router. One can from each router ping the ethernet interface of the other
router. I would predict that this is about all one can do, given this
configuration. In other words, if I had a live ethernet off my router, I
would be unable to ping any host on that subnet from the other router.
In any case, I believe I have demonstrated that the basic premise is true -
that one can have two routers configured so that all interfaces (within
certain limitations) are on the same subnet. But the end result is not what
the original question asked to accomplish. Without bridging one cannot have
all hosts on both sides reachable from the other side.
All of this, of course, is leaving me quite curious about how the ip
unnumbered process really works - what it is that happens on the logic
level. And I can more labs out there to help me understand some of the
things I predict will or won't happen if I do further testing, trying to run
real traffic across the connections.
It's getting late and so I bid you all good night.
Chuck
P.S. I will have the routers back on line for a while. Hope to catch up on
some long overdue experiments, including some fun stuff for the group.
-----Original Message-----
From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 11:48 AM
To: 'Chuck Larrieu'
Subject: RE: Quick Puzzle
Thanks Chuck,
Yes that was what I was looking for.
Does there have to be a loopback at one of the routers, or could I do as
follows:
Router1:
Serial0
Ip address 172.16.1.1 255.255.0.0
Ethernet 0
Ip unnumbered serial0
Router2:
Serial0
Ip address 172.16.2.2 255.255.0.0
Ethernet 0
Ip unnumbered serial0
???, and if yes, what is the loopback used for???
Thanks,
Ole
~~~~~~~~~~~~~~~~~~~~~~~~~~
Ole Drews Jensen
Systems Network Manager
CCNA, MCSE, MCP+I
RWR Enterprises, Inc.
[EMAIL PROTECTED]
~~~~~~~~~~~~~~~~~~~~~~~~~~
-----Original Message-----
From: Chuck Larrieu [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 1:11 PM
To: Ole Drews Jensen
Subject: RE: Quick Puzzle
I sent the following out, but you weren't on the recipient list. With the
way the list has been misbehaving the last couple of days, who knows when it
will port:
--------------------Copied Message-----------------
I looked over the config at the link. I am not sure that IRB is what the
original question revolved around. I thought I had understood it to be more
like:
Loopback 0
Ip address 172.16.1.1 255.255.0.0
Ethernet0
Ip unnumbered loopback0
Serial0
Ip unnumbered loopback0
Thus giving two different interfaces addresses on the same network. By
extension, the other side of the connection to serial0, being on the same
network, makes that link a bridge link rather than a router link.
OtherRouter
Serial0
Ip address 172.16.2.2 255.255.0.0
Ethernet 0
Ip unnumbered serial0
So that you end up with a topology of
LAN----router-----Router------LAN
And every interface is part of the same LAN, i.e. 172.16.0.0/16, in this
example.
Ole- is that what you were asking?
Chuck
-----Original Message-----
From: Ole Drews Jensen [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 10:58 AM
To: 'Chuck Larrieu'; Ole Drews Jensen; 'Matt'; [EMAIL PROTECTED]
Subject: RE: Quick Puzzle
:-)
I always like to see if I can get to a solution in at least one different
way than the most likely; Sometimes it turnes out to be more efficient like
in this example.
If you want to multiply X with 20 on your computer, you could ask it to do
it like this
Result := X * 20;
But it would actually be done faster, and thereby use less instructions, to
do it like this
Result := (X shl 4) + (X shl 2);
Shifting bits left (or right) and adding takes up less instructions than the
multiply function.
I know this is about 788 lightyears away from setting up a router as a
bridge, but I am just trying to draw a parallel.
Ole
~~~~~~~~~~~~~~~~~~~~~~~~~~
Ole Drews Jensen
Systems Network Manager
CCNA, MCSE, MCP+I
RWR Enterprises, Inc.
[EMAIL PROTECTED]
~~~~~~~~~~~~~~~~~~~~~~~~~~
-----Original Message-----
From: Chuck Larrieu [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 12:47 PM
To: Ole Drews Jensen; 'Matt'; [EMAIL PROTECTED]
Subject: RE: Quick Puzzle
What is it Howard likes to say? What is the problem you are trying to
create? :->
-----Original Message-----
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED]] On Behalf Of
Ole
Drews Jensen
Sent: Monday, July 10, 2000 9:54 AM
To: 'Matt'; [EMAIL PROTECTED]
Subject: RE: Quick Puzzle
Hmm, interesting.
Could you by doing so on two routers commicating with each other make them
work like a bridge?
Ole
~~~~~~~~~~~~~~~~~~~~~~~~~~
Ole Drews Jensen
Systems Network Manager
CCNA, MCSE, MCP+I
RWR Enterprises, Inc.
[EMAIL PROTECTED]
~~~~~~~~~~~~~~~~~~~~~~~~~~
-----Original Message-----
From: Matt [mailto:[EMAIL PROTECTED]]
Sent: Monday, July 10, 2000 11:40 AM
To: [EMAIL PROTECTED]
Subject: Re: Quick Puzzle
Make one unnumbered to the other. If you have an IP address configured on
the Serial0 port, go to interface config mode for the Ethernet0 and enter
the command:
"ip unnumbered Serial 0"
Matt
""Kenny Sallee"" <[EMAIL PROTECTED]> wrote in message
00a701bfea31$b4186d20$48a8a8c0@ksallee">news:00a701bfea31$b4186d20$48a8a8c0@ksallee...
How can you configure the same IP subnet on more than one interface in a
Cisco router?
Kenny
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