Cisco: Follow the network path / route and what devices it’s traveling though to find a particular host on the LAN.

Follow and find the network path / route and what devices it’s traveling though to reach a particular host on the LAN.

The network I work on has a number of Cisco routers and Cisco switches along with Ciscco ASA with many servers and workstations on it, along with many subnets using vlsm. The routing table is out of date and I want to track down the routing paths to find out if the routes are still needed or if there is a better path that can be used along with documenting the network. I need to rely on the routing table, since there is no documentation to follow such as network diagrams, ip address logs ect..

I’d like to find a good lab with gns3 or at least some good documentation explaining how to track down routing paths. I’m going to first track down the static routes, and then OSPF and BGP routes.

I understand the technology, but just need some good examples to go by for doing this.

Thank you,
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dsterlingAuthor Commented:
I have something to add, icmp is blocked on some of the devices and can't be unblocked with out a lot of approval, which will take too long and may not be approved.
OSPF and BGP routes are by definition "good" unless they were created by redstributing static routes into them. So I think once you've worked out which of those should go, you'll be OK.

Now, static routes don't rely on other routers. They just sit there. So you can't find the "source" of a static route. What you need to will be in your live network, not in a lab. You have to visit the next hop of a static route and determine whether that route is good.

Pretty much if you are using a dynamic routing protocol and it's correctly configured, static routes should be nearly non-existent- usually only a default static route would be required. Exceptions are if you have a device you are routing to which doesn't support dynamic routing. So I would start at the borders of your network and work inward to get OSPF working correctly. If you can see the route in "show ip ospf database" then you don't need a static route.
Soufiane Adil, Ph.DIT, Network Architect - CCNP/CCDPCommented:

You can use NetBrain, all you need is to load your configs and NetBRain will draw the network map for you.

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dsterlingAuthor Commented:
Static routes do exist on the network, and I want to find out where they go to determine if they are needed. I don't agree that static routes can't be tracked down, you can follow the external interface the route is using and see where it leads. For example: What if there is a layer 3 vlan on say router 3 and router 3 is connected to router 2 that is connected to router 1 that has the static routes going to  the layer 3 vlan on router 3 out of the serial interface connected to router 2. I know the interfaces should be in OSPF, but that is part of what I'm doing, determining what static routes are needed. I work on an Enterprise network  and I'm in the process of making network maps that will be used to make the necessary changes to make the network more efficient. There is a large routing table on the Data Center, Core and External switches and routers. Approval must be done in order to make any change on the network so tracking down the routes is important.

What about BGP, there is the BGP table and the OSPF database that can be used to determine where the routes lead.

Also I can't install any software with out going through a approval process and based on  the request for programs like Solar Winds, Cisco Works, and the strict security on the network, it is a small chance that it will happen and if it did, it would be a lengthily process and I don't' have time for that, so installing NetBrian on the network is not going to happen.

Soufiane Adil, Ph.DIT, Network Architect - CCNP/CCDPCommented:
Can you share with us your network map and configs, to have an idea about the issue?

dsterlingAuthor Commented:
OK, I'll try to get the info this week. Thank you
I didn't say that the static routes can't be tracked down, I said that you can't find the "source." Maybe it's a semantic issue. Anyway, I think we were saying the same thing:
1. Hopefully you know your network well enough that if you see  static route, you know where that network resides. If you do, you can work backwards from the destination to see if it also exists in OSPF (if it doesn't, put it in) and/or where static routes exist for it.
2. If you don't know where the destination network resides, go to the next hop of the static route and see if the destination is reachable from there. If not, remove the static route because it's invalid anyway. If it is reachable, is it via another static route or is it via OSPF (or BGP)?
3. If it's via OSPF, is it a redistributed static route or is it learned via network statements? I personally hate "redistribute connected" as a means of putting routes in OSPF because all routes look external and the default metric calculations are much less granular.

I don't honestly see the point of posting a network map here; it won't tell us where the static routes are or whether they're valid. If you make it detailed enough to show us what kind of routes point where then you've already done the work you need to do.

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