some networking questions

[jes]

I am taking some CCNA training right now. I have been able to Google the answers to most of my questions that are not answered by the reading material but have not been able to find out why static routes cannot be used as child routes. Does anyone reading this know?

[Variable]

I wasn't sure what you meant so I did some digging. A child route is one created by a routing protocol. A routing protocol creates routes by learning about what networks are around it. A static route is defined manually and permanent until manually removed.

[jes]

Here (http://jesse.sasktelwebsite.net/Untitled.jpg) is a routing table with one parent rout and then six child routes. Three of them static, two directly connected and one collected by RIP. I understand that the static routes are invalid. I am wondering if there is anyone here that knows why they are invalid.

[Variable]

Why are they invalid? Is this a test question you found and don't know why the answer is what they say? Is there anymore to the question other than that image? It may want you to put the interface instead of the intermediate IP. If the 192 network lived on the other side you would think RIP would have some routes.

[jes]

sorry. I forgot to post the whole thing. (http://jesse.sasktelwebsite.net/Untitled.jpg)
A friend of mine is doing the same thing as me and says that he thinks that he heard that static routes are invalid as child routes but doesn't know why.

P.S. The answer stated is option 2.

[Ghost_Hacker]

Once thing I can see ......


Since you are using RIP the static routes must be configured with an admin cost higher then 120. Your example shows them with their default of 1. This default value, if not changed, screws up RIP updates to your router.

Variable may have other insights.

Good luck :)

[jes]

Interesting. How does that interfere with the rip updates?

I didn't know that it was possible to change the administrative distance. I thought that the router just decided based on how the route is configured. To tell you the truth, I have never fully understood the usage of administrative distance/cost.

[Variable]

A static route can be a child route.
When a network address doesn't follow the default classful mask, a parent route is created. The default mask for 172 networks is 255.255.0.0 or /16 not, a /24, that would be a class C. So since the 172 network has a class C mask, there is an entry as a parent route. Whenever a parent route is created a child route is created. If the route can be resolved to an interface it is an Ultimate route but it can be a child. There is no further recursive lookup needed. So the answer would be there is at least one parent and one child route. 172.16.2 -172.16.4 are child routes.

The 192. statics reference an interface. So they would be ultimate routes. 192.168.3.0 is not a child route of 172 it was learned from RIP.

This is my understanding of the issue.

As for RIP is looks correct to me. it should be 120/1

This doesn't look like VLSM

[Ghost_Hacker]

Interesting. How does that interfere with the rip updates?

I didn't know that it was possible to change the administrative distance. I thought that the router just decided based on how the route is configured. To tell you the truth, I have never fully understood the usage of administrative distance/cost.


It effects how the router uses the routes it learns via RIP. A static route with an AD (administrative distance) of one will always override a RIP route with its AD of 120 (or any route that is not directly connected and therefore has an AD of 0). What this means is that those static routes will take precedent over any routes learned via RIP on that router when routing packets out its interfaces. So accuracy of those static routes becomes very important.

Also you might want to use floating static routes. Floating static routes are used as backup routes if the primary dynamic route is removed from a routing table for what ever reason (perhaps it went down). So in this case you would use 121 as the AD for a static route causing it to "float" in the routing table and only be used when the primary route failed and was removed for the table.


In small networks these issues may not matter in larger ones it might.


One way to change the AD is when you enter the static route. Example:

ip route 172.10.10.10 255.255.255.0 192.10.10.10 150

Where "150" = the AD for this route.


Hope this helps :)

[Ghost_Hacker]

....

This is my understanding of the issue.

As for RIP is looks correct to me. it should be 120/1

This doesn't look like VLSM

Yeap, the only way I can see for the static routes to be invalid is the use of the default AD of 1 when using a routing protocol. Which in this case is RIP.

[jes]

There is alot of interesting information here but I don't think that I am fully understanding yet.

I know that option 1 is out because the AD of 120 indicates RIP.
Option 4 would actually point to serial 0/0/0.
Option 2 seems right but I don't see why is option 3 invalid

[Ghost_Hacker]

Using the info provide by Variable we know that only a network with a subnet mask that is of a different class then the IP would indicate will become a parent route and it subnets become child routes..

192.x.x.x is a class C network so its subnet mask of "/24" is correct (/24 is class c subnet). So there is no parent/child relation ship for the "192" networks.

[jes]

Oh, I think that I understand now. The 172 are child but not the 192. Thanks.

I should have suspected that. I have a nasty habit of looking for a very complicated solution. I tend to over-think things. I thought that there would be some far-reaching consequence of static routes that renders them invalid.

[Variable]

The 192 networks are child routes as noted by the show ip route. But .3 is not a directly connected interface as the other two are. Think of the Parent route as 172.16.0.0 as the top of the routing table, the router builds a top down hierarchy of how to route. The 192.168.2 and 4 are the IP addresses of the interface. They also have a default mask /24 for their Class C network. SO there is no parent route for 192.168.0.0 created for 192 it falls under the 172.16. The parent route is created automatically when a network does not follow their default mask. I think the only problem with option 3 is that the RIP created route is not a "child" route.

Much of what you learn for CCNA will not be used much, I remember spending two semesters on classful subnetting only to learn that it is a waste of time because now the standard is VLSM i.e. classless. If you are using a classful routing protocol like RIP then you need to know how it works. Why anyone would use RIP version 1 I don't know.


Another thing to recognize is, what are common cisco classful and classless routing protocols. If you are using a classless routing protocol, how does the show IP route look different when compared to using a classful protocol. The answer about EIGRP would be a easy one to rule out if you understood this.

[jes]

I see. I am taking the new version 4.0 and the only reason that we study any classless routing now is to better understand the class and things like this question.

Another question that I have that is in this area is "How does the IP Classless command or the no Ip classless command affect weather the router uses the default rout or not?". (Like this (http://jesse.sasktelwebsite.net/Untitled.jpg))

[Ghost_Hacker]

If I remember my Cisco stuff correctly :) A Cicso router will drop a packet with a subnet destination that is not in its table. So when using default routing its best to use the "IP classless" command to ensure these packets are not dropped and will be sent out the default route or interface.

Hope this helps :)

[jes]

If you remember your Cisco stuff? What do you do now?

[Ghost_Hacker]

If you remember your Cisco stuff? What do you do now?

Not sure if you mean "what work i do now" or "what you do after setting up the ip classless command" :D but....

I don't do anything really:D, I am currently in the middle of one of my "year long vacations" which I take every 5 years or so.

Normally I do systems engineering/network engineering work and IT security consulting. I also sometimes do server/network administration work if the job has access to new applications or tech I have not worked with before.

My Cisco know how is limited because I don't do hands on work with them though I have been thinking of getting my certs (CCNA and then the CCNP) as there are some interesting "cisco" jobs out there at the moment.

So if you have more Cisco questions please post them as they help with my studies too :)

[jes]

Do you have Packet Tracer? I have created OSPF and EIGRP networks and am not sure why they don't work.

[Ghost_Hacker]

Nope don't have packet tracer. I am looking to use Dynagen.
What version of Packet Tracer do you have?

[jes]

I have 4.1
Is Dynagen compatible?

[Ghost_Hacker]

Yeap, it has much the same features and uses as packet tracer. Here is the dynagen tutorial (http://www.dynagen.org/tutorial.htm)

I'll have to see if I can find PT 4.1 and set it up :)

[jes]

I would give you Packet Tracer but I think that it is Cisco proprietary software and I don't want to violate any copyrights. I think that I can give you the .pkt files once you have the program though. Legally speaking, I think that it is just the same thing as freely distributing a .doc or a .pdf file.

If I setup a VLAN in Packet Tracer, how can I test it? I understand that the purpose of a VLAN is to separate broadcast domains. How can I check that broadcasts are not moving from VLAN10 to VLAN11 ?

[Ghost_Hacker]

I would give you Packet Tracer but I think that it is Cisco proprietary software and I don't want to violate any copyrights. I think that I can give you the .pkt files once you have the program though. Legally speaking, I think that it is just the same thing as freely distributing a .doc or a .pdf file.

I agree sharing that file shouldn't be a problem. Thanks!:cool:



If I setup a VLAN in Packet Tracer, how can I test it? I understand that the purpose of a VLAN is to separate broadcast domains. How can I check that broadcasts are not moving from VLAN10 to VLAN11 ?

Hmm not sure how to check in PT. Normally you would just use sniffer or check the switch itself. I would suspect PT has some sorta packet trace function, but I still have not got around to setting it up yet.

EDIT From what i have read PT should have a packet sniffer built in. You can use that to see if broadcast traffic is moving across VLANs. Of couse this depends on what kinda broadcast traffic you can
simulate in PT.

[jes]

http://jesse.sasktelwebsite.net/VLAN.7z

I don't remember how to post a file like this. All that you can see is the giberish. I think that I need some extra HTML code so it can be downloaded. Is that right?