From: Yasser Aly (blackyeyes00@hotmail.com)
Date: Mon Feb 23 2004 - 11:19:30 GMT-3
Hi Colin,
Here is an example,
R2 (S0)-----Frame-Relay------(S0) R3 (S1)------Frame-Relay--------(S0) R5
OSPF area 0 is running between R2 and R3, ISIS is running over Frame-Relay
between R3 and R5.
R5 & R3 are in a single ISIS area.
R2 in another ISIS area.
R2 and R3 are forming ISIS Layer 2 adjacency.
Now here it goes:
1) R5 is advertising its loopbck address via ISIS, R3 will learn it as an
ISIS route with admin distance 115.
2) This route will be passed to R2.
3) On R2 redistribution between ISIS and OSPF is happening.
4) R3 will learn loopback of R5 again but this time via OSPF with admin 110.
5) R3 now will have 2 routes one via OSPF and the other via ISIS. It will
prefer the OSPF route with next-hop pointing to R2, R2 inturn is having an
ISIS route with next-hop pointing to R3.
This will result in a routing loop to reach this loopback address of R5.
While this routing loop exists, debug IP routing is not showing anything in
its output reflecting this.
This problem was solved by altering the admin distance on R3 to prefer ISIS
routes over OSPF, such that R3 will not install the OSPF route learned from
R2.
In such a case how can you detect the routing loop ??
Regards,
Yasser
>From: "Fowlie, Colin" <Colin.Fowlie@aliant.ca>
>
>Do you have a particular specific example where you've seen this?
>(Topology - Protocols etc.) You mention that "debug ip routing" doesn't
>detect the loop while it exists. If the loop only exists for a certain
>period of time, and then is resolved by the IGP, then this would should up
>in the debug output at the point where the loop is created/resolved. i.e.
>you should see a route-flap.
>
>Again, if you can provide an example where you ran into this perhaps that
>would shed more light on the situation.
>
>-Colin
>
>-----Original Message-----
>From: Yasser Aly [mailto:blackyeyes00@hotmail.com]
>Sent: Monday, February 23, 2004 9:23 AM
>To: Fowlie, Colin; karim_ccie@hotmail.com; msnyder@revolutioncomputer.com;
>ccielab@groupstudy.com
>Subject: RE: Routing loops detection [Re: Checking the Lab Work]
>
>
>Hi Colin,
>
>I tried using this command before and in some cases it will not detect the
>loop while it exists.
>
>An example when Two routers consider eachother as the next-hop for a
>certain
>destination, here no routing updates are representing the loop where if you
>did a traceroute you will detect it.
>
>Regards,
>Yasser
>
> >From: "Fowlie, Colin" <Colin.Fowlie@aliant.ca>
> >Reply-To: "Fowlie, Colin" <Colin.Fowlie@aliant.ca>
>
> >
> >I would recommend running "debug ip routing" and then watching for
>flapping
> >routes. This is also helpful to watch the effect of your routing
>protocol
> >redistribution.
> >
> >-Colin
> >
> >-----Original Message-----
> >From: Karim [mailto:karim_ccie@hotmail.com]
> >Sent: Saturday, February 21, 2004 4:17 PM
> >To: Yasser Aly; msnyder@revolutioncomputer.com; ccielab@groupstudy.com
> >Subject: Routing loops detection [Re: Checking the Lab Work]
> >
> >Hi all,
> >I have the same concern about detecting routing loops especially after
> >finishing the redistribution configurations.
> >Could someone help please.
> >
> >Regards,
> >Karim.
> >
> >
> >----- Original Message -----
> >From: "Yasser Aly" <blackyeyes00@hotmail.com>
> >To: <msnyder@revolutioncomputer.com>; <ccielab@groupstudy.com>
> >Sent: Friday, February 20, 2004 8:28 PM
> >Subject: RE: Checking the Lab Work
> >
> >
> > > Hi group,
> > >
> > > Would you kindly share us with your visions on time saving
>techniques
> >to
> > > detect a routing loop ?
> > >
> > > Regards,
> > > Yasser
> > >
> > >
> > > >From: "Michael Snyder" <msnyder@revolutioncomputer.com>
> > > >You don't.
> > > >
> > > >This is simply checking the routing table for present routes.
> > > >
> > > >A hybrid technique would be needed to test reachability and routing
> > > >table contents.
> > > >
> > > >
> > > >
> > > >-----Original Message-----
> > > >From: Yasser Aly [mailto:blackyeyes00@hotmail.com]
> > > >Sent: Friday, February 20, 2004 12:10 PM
> > > >To: msnyder@revolutioncomputer.com; ccielab@groupstudy.com
> > > >Cc: ahmed.mustafa@sbcglobal.net
> > > >Subject: RE: Checking the Lab Work
> > > >
> > > >
> > > >Hello,
> > > >
> > > > I have two questions:
> > > >
> > > >1) How to verify reachability for all your routes on the 3550 switch.
>I
> > > >tried tclsh but the command was not accepted on it ?
> > > >
> > > >2) If you rely on the procedure described below it will be
>misleading.
> > > >Example, if you have a routing loop for a certain route, you will
>have
> >a
> > > >
> > > >route in the sh ip route for the looped route, however you will not
>be
> > > >able
> > > >to detect that it is looped and might think everything is ok if you
> >rely
> > > >
> > > >only that the route show up in the routing table.
> > > >
> > > >This leads to the question: How to detect that you have a routing
>loop
> > > >with
> > > >one of your routes ?
> > > >
> > > >Regards,
> > > >Yasser
> > > >
> > > > >From: "Michael Snyder" <msnyder@revolutioncomputer.com>
> > > > >
> > > > >Here's a repost of the igp grading script I wrote last year.
> > > > >
> > > > >It's for people with a rack full of 2500`s and don't have access to
> > > > >tclsh.
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >I was working on a lab this morning, and for some reason my three
>way
> > > > >redistribution wasn't working.
> > > > >
> > > > >After jumping router to router for 30 minutes, I thought gee I wish
>I
> > > > >had a command to show me every missing route.
> > > > >
> > > > >I made a script to do this; I'll walk you thru how I composed the
> > > > >script. It took me about 5 minutes.
> > > > >
> > > > >Here's some benefits of the script.
> > > > >
> > > > >1) Can't be fooled by a default route.
> > > > >2) Can't be fooled by the wrong mask size.
> > > > >3) Assumes that the route should be present.
> > > > >
> > > > >Generates output only if it's missing.
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >First I did a `show run | i ip address`
> > > > >
> > > > >And pasted the results to notepad from every router.
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > > ip address 170.1.1.1 255.255.255.255
> > > > > ip address 150.50.200.1 255.255.255.0
> > > > > ip address 170.1.150.1 255.255.255.0
> > > > >
> > > > > ip address 170.1.2.2 255.255.255.255
> > > > > ip address 172.16.1.1 255.255.255.0
> > > > > ip address 172.16.3.1 255.255.255.0
> > > > > ip address 172.16.2.1 255.255.255.0
> > > > > ip address 172.16.0.1 255.255.255.0
> > > > > no ip address
> > > > > no ip address
> > > > > ip address 170.1.100.2 255.255.255.0
> > > > > ip address 170.1.150.2 255.255.255.0
> > > > > ip address 150.50.9.5 255.255.255.252
> > > > >
> > > > > ip address 170.1.4.4 255.255.255.255
> > > > > ip address 192.168.10.1 255.255.255.0
> > > > > no ip address
> > > > > ip address 170.1.100.4 255.255.255.0
> > > > > no ip address
> > > > >
> > > > > ip address 170.1.5.5 255.255.255.255
> > > > > ip address 170.1.200.5 255.255.255.224
> > > > > no ip address
> > > > > ip address 170.1.100.5 255.255.255.0
> > > > > no ip address
> > > > > no ip address
> > > > >
> > > > > ip address 170.1.6.6 255.255.255.255
> > > > > ip address 170.1.200.6 255.255.255.224
> > > > > no ip address
> > > > > ip address 170.1.100.6 255.255.255.0
> > > > > ip address 170.1.32.6 255.255.255.0
> > > > > no ip address
> > > > >
> > > > > ip address 170.1.7.7 255.255.255.255
> > > > > ip address 170.1.200.7 255.255.255.224
> > > > > ip address 170.1.24.7 255.255.255.0
> > > > >
> > > > > ip address 170.1.8.8 255.255.255.255
> > > > > ip address 150.50.4.8 255.255.255.0
> > > > > ip address 170.1.24.8 255.255.255.0
> > > > >
> > > > > ip address 170.1.9.9 255.255.255.255
> > > > > ip address 170.1.32.9 255.255.255.0
> > > > > no ip address
> > > > > ip address 170.1.15.9 255.255.255.192
> > > > >
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >
> > > > >Next in notepad, I did a replace all of `no ip address` with a null
> > > > >string. Then I went thru the listing deleting the empty lines.
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > > ip address 170.1.1.1 255.255.255.255
> > > > > ip address 150.50.200.1 255.255.255.0
> > > > > ip address 170.1.150.1 255.255.255.0
> > > > > ip address 170.1.2.2 255.255.255.255
> > > > > ip address 172.16.1.1 255.255.255.0
> > > > > ip address 172.16.3.1 255.255.255.0
> > > > > ip address 172.16.2.1 255.255.255.0
> > > > > ip address 172.16.0.1 255.255.255.0
> > > > > ip address 170.1.100.2 255.255.255.0
> > > > > ip address 170.1.150.2 255.255.255.0
> > > > > ip address 150.50.9.5 255.255.255.252
> > > > > ip address 170.1.4.4 255.255.255.255
> > > > > ip address 192.168.10.1 255.255.255.0
> > > > > ip address 170.1.100.4 255.255.255.0
> > > > > ip address 170.1.5.5 255.255.255.255
> > > > > ip address 170.1.200.5 255.255.255.224
> > > > > ip address 170.1.100.5 255.255.255.0
> > > > > ip address 170.1.6.6 255.255.255.255
> > > > > ip address 170.1.200.6 255.255.255.224
> > > > > ip address 170.1.100.6 255.255.255.0
> > > > > ip address 170.1.32.6 255.255.255.0
> > > > > ip address 170.1.7.7 255.255.255.255
> > > > > ip address 170.1.200.7 255.255.255.224
> > > > > ip address 170.1.24.7 255.255.255.0
> > > > > ip address 170.1.8.8 255.255.255.255
> > > > > ip address 150.50.4.8 255.255.255.0
> > > > > ip address 170.1.24.8 255.255.255.0
> > > > > ip address 170.1.9.9 255.255.255.255
> > > > > ip address 170.1.32.9 255.255.255.0
> > > > > ip address 170.1.15.9 255.255.255.192
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >
> > > > >This lab uses a summary address of 172.16.0.0/22, so I chose to
>pull
> > > >out
> > > > >the 172.16.1.1/24 routes and use the summary instead.
> > > > >
> > > > >Here's a important part, I needed a unique post-delimiter on the
> >ends
> > > > >of the statements for text search and replace later. So I appended
> >the
> > > > >` char to the ends of the statements by hand. Each statement
>begins
> > > >the
> > > > >same `ip address` text, so I don't need a pre-delimiter here.
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >
> > > > >
> > > > > ip address 170.1.1.1 255.255.255.255 `
> > > > > ip address 150.50.200.1 255.255.255.0 `
> > > > > ip address 170.1.150.1 255.255.255.0 `
> > > > > ip address 170.1.2.2 255.255.255.255 `
> > > > > ip address 172.16.0.0 255.255.252.0 `
> > > > > ip address 170.1.100.2 255.255.255.0 `
> > > > > ip address 170.1.150.2 255.255.255.0 `
> > > > > ip address 150.50.9.5 255.255.255.252 `
> > > > > ip address 170.1.4.4 255.255.255.255 `
> > > > > ip address 192.168.10.1 255.255.255.0 `
> > > > > ip address 170.1.100.4 255.255.255.0 `
> > > > > ip address 170.1.5.5 255.255.255.255 `
> > > > > ip address 170.1.200.5 255.255.255.224 `
> > > > > ip address 170.1.100.5 255.255.255.0 `
> > > > > ip address 170.1.6.6 255.255.255.255 `
> > > > > ip address 170.1.200.6 255.255.255.224 `
> > > > > ip address 170.1.100.6 255.255.255.0 `
> > > > > ip address 170.1.32.6 255.255.255.0 `
> > > > > ip address 170.1.7.7 255.255.255.255 `
> > > > > ip address 170.1.200.7 255.255.255.224 `
> > > > > ip address 170.1.24.7 255.255.255.0 `
> > > > > ip address 170.1.8.8 255.255.255.255 `
> > > > > ip address 150.50.4.8 255.255.255.0 `
> > > > > ip address 170.1.24.8 255.255.255.0 `
> > > > > ip address 170.1.9.9 255.255.255.255 `
> > > > > ip address 170.1.32.9 255.255.255.0 `
> > > > > ip address 170.1.15.9 255.255.255.192 `
> > > > >
> > > > >
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >Here's the payoff. Using notepad, replace all `ip address` with
> >`show
> > > > >ip route` Also replace our delimiting char ` with `| i not`
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > > show ip route 170.1.1.1 255.255.255.255 | i not
> > > > > show ip route 150.50.200.1 255.255.255.0 | i not
> > > > > show ip route 170.1.150.1 255.255.255.0 | i not
> > > > > show ip route 170.1.2.2 255.255.255.255 | i not
> > > > > show ip route 172.16.0.0 255.255.252.0 | i not
> > > > > show ip route 170.1.100.2 255.255.255.0 | i not
> > > > > show ip route 170.1.150.2 255.255.255.0 | i not
> > > > > show ip route 150.50.9.5 255.255.255.252 | i not
> > > > > show ip route 170.1.4.4 255.255.255.255 | i not
> > > > > show ip route 192.168.10.1 255.255.255.0 | i not
> > > > > show ip route 170.1.100.4 255.255.255.0 | i not
> > > > > show ip route 170.1.5.5 255.255.255.255 | i not
> > > > > show ip route 170.1.200.5 255.255.255.224 | i not
> > > > > show ip route 170.1.100.5 255.255.255.0 | i not
> > > > > show ip route 170.1.6.6 255.255.255.255 | i not
> > > > > show ip route 170.1.200.6 255.255.255.224 | i not
> > > > > show ip route 170.1.100.6 255.255.255.0 | i not
> > > > > show ip route 170.1.32.6 255.255.255.0 | i not
> > > > > show ip route 170.1.7.7 255.255.255.255 | i not
> > > > > show ip route 170.1.200.7 255.255.255.224 | i not
> > > > > show ip route 170.1.24.7 255.255.255.0 | i not
> > > > > show ip route 170.1.8.8 255.255.255.255 | i not
> > > > > show ip route 150.50.4.8 255.255.255.0 | i not
> > > > > show ip route 170.1.24.8 255.255.255.0 | i not
> > > > > show ip route 170.1.9.9 255.255.255.255 | i not
> > > > > show ip route 170.1.32.9 255.255.255.0 | i not
> > > > > show ip route 170.1.15.9 255.255.255.192 | i not
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >Ok, lets try it on R4.
> > > > >
> > > > >I use four terminal windows, so I cut and paste to all four at
>once,
> > > >and
> > > > >read the results when done. It's really telling when you see the
> >same
> > > > >missing route on three of the four routers.
> > > > >
> > > > >Another thing, if route shouldn't show up on any router, replace
>the
> >`i
> > > > >not` with `e not`
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >R4#
> > > > >R4#
> > > > >R4# show ip route 170.1.1.1 255.255.255.255 | i not
> > > > >R4# show ip route 150.50.200.1 255.255.255.0 | i not
> > > > >% Network not in table
> > > > >
> > > > >R4# show ip route 170.1.150.1 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.2.2 255.255.255.255 | i not
> > > > >R4# show ip route 172.16.0.0 255.255.252.0 | i not
> > > > >R4# show ip route 170.1.100.2 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.150.2 255.255.255.0 | i not
> > > > >R4# show ip route 150.50.9.5 255.255.255.252 | i not
> > > > >% Network not in table
> > > > >
> > > > >R4# show ip route 170.1.4.4 255.255.255.255 | i not
> > > > >R4# show ip route 192.168.10.1 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.100.4 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.5.5 255.255.255.255 | i not
> > > > >R4# show ip route 170.1.200.5 255.255.255.224 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.100.5 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.6.6 255.255.255.255 | i not
> > > > >R4# show ip route 170.1.200.6 255.255.255.224 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.100.6 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.32.6 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.7.7 255.255.255.255 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.200.7 255.255.255.224 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.24.7 255.255.255.0 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.8.8 255.255.255.255 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 150.50.4.8 255.255.255.0 | i not
> > > > >% Network not in table
> > > > >
> > > > >R4# show ip route 170.1.24.8 255.255.255.0 | i not
> > > > >% Subnet not in table
> > > > >
> > > > >R4# show ip route 170.1.9.9 255.255.255.255 | i not
> > > > >R4# show ip route 170.1.32.9 255.255.255.0 | i not
> > > > >R4# show ip route 170.1.15.9 255.255.255.192 | i not
> > > > >R4#
> > > > >
> > > > >
> > > >
> > >-----------------------------------------------------------------------
> > > >-
> > > > >--
> > > > >
> > > > >There's my missing routes!!! For some reason rip isn't making it
>to
> > > > >ospf on R4.
> > > > >
> > > > >
> > > > >-----Original Message-----
> > > > >From: Ahmed Mustafa [mailto:ahmed.mustafa@sbcglobal.net]
> > > > >Sent: Wednesday, February 18, 2004 9:44 PM
> > > > >To: ccielab@groupstudy.com
> > > > >Subject: Checking the Lab Work
> > > > >
> > > > >Guys,
> > > > >
> > > > >What is the easiest way to check the lab work. This is the most
> > > > >important
> > > > >task especially if one is taking a real lab.
> > > > >
> > > > >I mean what is the best way to find out that you are seeing all the
> > > > >routes in
> > > > >your routers that are you are supposed to be seeing, and pinging
>all
> > > >the
> > > > >interfaces making sure that there is no loss of connectivity. I
>know
> > > > >that one
> > > > >can do this from each router to see what routes are seen and
>whether
> > > > >they are
> > > > >pingable
> > > > >Is there any work around?
> > > > >
> > > > >Thanks,
> > > > >
> > > > >Ahmed
> > > > >
> > > >
> > >_______________________________________________________________________
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