Dynamic routing issue

[Bruno Silva]

Hello,

well, my question is: I have one central route (Cisco Catalyst 3750G-48TS-S) and twenty Switch with layer three ios (Cisco 3560G-24) conected in star topology....

What i want to know is, how central router can communicate with just another router (Cisco 1841) that is behind any 3560G layer three switch?

the cisco 1841 is always the same router that could be behind any other cisco 3560G switch.

Thanks a lot for your patience!

Bruno

[Jon Marshall]

edited

[Bruno Silva]

What do you mean with that?

[Jon Marshall]

Bruno

No you are not wrong with your example. You can't do this although i understand why you are trying to do it.

In effect you want a sort of plug and play setup where an 1841 could be plugged into any switch and it will work without manual intervention.

Here is what i don't understand. Lets say you use the same vlan/IP subnet for one 1841 on all switches. You are then advertising that back to the 7301 and it sees equal cost routes to all your switches so it doesn't know which one to send packets to.

But a the L3 vlan interface will only be up on the 3560 if -

1) an access port in that vlan is up/up

or

2) a trunk link allowing vlan 506 is up/up

If neither of the above were true the L3 vlan interface would be down in which case EIGRP should  not announce a route to that subnet back to the 7301. So what is keeping that L3 vlan interface up/up on each 3560  ? From your config of the 3560 you have this -

interface GigabitEthernet0/5

description Wimax

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 500-508

switchport mode trunk

what is the above port connecting to and more importantly is it up/up ?

Jon

[Bruno Silva]

Exactly Jon... what i want is a sort of plug and play setup where an 1841 could be plugged into any switch and it will work without manual intervention. yes, yes, yes!

Yes, for one 1841 i use the same vlan/IP subnet on all switches. For instance, to 1841#6 i have Vvlan 506 (ip 10.10.56.0/24).

My config on the 3560 wich is:

interface GigabitEthernet0/5

description Wimax

switchport trunk encapsulation dot1q

switchport trunk allowed vlan 500-508

switchport mode trunk

The above port connecting to and more importantly is it up/up is VLAN 500 that is wimax equipment is bridge mode to connect to another wimax equipment in bridge mode to connect to 1841 router fo mobile unit.

The other ones L3 vlan interfaces (501-508) will only be up on respective 3560 if one mobile unit 1841 is connected to.

Bruno.

[Jon Marshall]

Bruno

It won't work because the trunk link ie. gi0/5 is always up/up. Because of this the L3 vlan interface for vlan 506 is up and so EIGRP announces this route to the 7301. This happens on all your switches and that is why the 7301 sees routes to vlan 506 via all port channel subinterfaces.

Gi0/5 is up/up whether or not you have connected an 1841 at the other end - this is the case isn't it ?

The other ones L3 vlan interfaces (501-508) will only be up on respective 3560 if one mobile unit 1841 is connected to

Not sure i follow. If the trunk is up/up wihout an 1841 then the 3560s should be advertising all the vlan 501 - 508 subnets anyway. Are you saying they don't ?

Jon

[Bruno Silva]

Yep... this is the case! Gi0/5 is up/up whether or not i have connected an 1841 at the other end, and it shouldn't be like that.

I said: " The other ones L3 vlan interfaces (501-508) will only be up on respective 3560 if one mobile unit 1841 is connected to"... what i want to mean was: "With trunk up/up without an 1841 connected to it then the 3560s should not advertising all the vlan 501 - 508 subnets."

[Jon Marshall]

Bruno

With trunk up/up without an 1841 connected to it then the 3560s should not advertising all the vlan 501 - 508 subnets.

But it will unfortunately because the vey fact of the trunk being up means the L3 vlan interface is up and so EIGRP advertises the route. If the 1841 was actually plugged directly into the 3560 then what you want would work because the port would only come up when the 1841 was connected but you have WiMAX equipment connected to the 3560 and that is what brings the trunk link up.

There is now way around this that i know of.

That said, both the 3560 and the 1841 support EEM which allows you to run scripts on the device. There may be a way we could dynamically add the network statement for vlan 506 under the EIGRP config so it is only advertised when the 1841 is actually connected.  Of course i could be talking rubbish and it still may not be possible.

I know a person on these forums who is very good and knows EEM so i will drop him a line and ask him to join in this thread and see -

1) if there is anything i have missed

2) if there is a possibility of using EEM

Jon

[Bruno Silva]

THANKS A LOT, Jon!

just to confirm, in that case that i have 20 3560G routers with wimax connected, his 501 to 508 vlans will be announced by eigrp to 7301 central router, because trunk port is allways up/up and therefore 7301 will have so much routes to same vlan (501-508) as 3560G switches i have? And 7301 cannot decide what route take....

Ok... i'll wait for your friend EEM expert!

Once again, thanks for your precious help!

[Jon Marshall]

Bruno

I have sent a message to John but he may not see it for a while and he may not have the time. I suggest we leave it for a day or so and if he doesn't join the thread we can summarise what the issue is (i'll help with that if needed) and then we can post into the EEM forum.

But it's worth waiting a bit to see if John joins the thread.

Jon

[John Blakley]

Bruno/Jon,

Jon: Thank you for the kind words I truly hope I can be of at least a little help!

Bruno,

I've read through your thread, and you've been helped by one of the best on these forums (speaking of Jon). I have a couple of questions. First, let me see if I can sum up what I've read:

You connect the 1841 to 3560s at random places because the router is mobile?

Vlan 506 is your dedicated vlan for the router at all locations, or can it be any of the 501 - 508 vlans listed?

As Jon stated, vlans 501 - 508 are always up because the Wimax equipment is connected to a trunk port?

When you connect the 1841, is it always connected to the same port, or can that vary?

Taking the above into account, we need to figure out how we can get routes advertised when the router is connected only as I think (correct me if I'm wrong) you only use the vlan for when the router is connected and nothing else. Is that the case?

The vlan is up/up at all times because the wimax equipment is connected to the port. This switch (3560s?) is advertising its routes via eigrp always because the vlan is up/up. We need to have some way of determining when to launch a script. There has to be some event that we can identify, whether it be a port up event or some log entry that the script can watch to trigger the script. For example, if you told us that you always plug the router into fa0/1 on the switch, we could write the script to advertise the network that you want only when that interface is seen to come up. In that case, you'd probably want port security configured on the switch as well to protect the port from coming up unless it was the router.

This is going to be next to impossible though if you use the vlan for more than just this router. For example, if there is other equipment on that vlan that you have to take into account, you're going to need to advertise the subnet all the time regardless if the router is connected or not. Is this the case? If not, is there a way that you could dedicate a port (if you're not already) to the router at each location?

** Edit **

Do you have a diagram of one of the locations that you could share? If not, can you draw one up? It would be helpful to see how the 1841 connects to your other equipment.

HTH,
John

*** Please rate all useful posts ***

[Jon Marshall]

John

Firstly thanks for joining in, much appreciated. And yes, you have understood the issue perfectly.

And thanks for the compliment but in all honesty i have to say that the quality of your answers far surpasses much of what i contribute. I sound like i'm reminiscing but i remember answering some of your questions when i was last active in the forums before and now when i read your posts i am the one who is learning off you.

So, no pressure to sort this problem out then

Jon

[Bruno Silva]

John,

i realized that Jon have perfectly control about this thread, it was a superkind and gratefull helping. the truth is, Jon is a master on this issue.

Sorry, i'm not used to be in this foruns and did not know that was possible to rate the posts. I will!

Well, i'll answer you in bold:

You connect the 1841 to 3560s at random places because the router is mobile? B: Yes. 1841 router is a mobile router.

Vlan 506 is your dedicated vlan for the router at all locations, or can it be any of the 501 - 508 vlans listed?

B: Yes. Vlan 506 is mine vlan dedicated for the router#6 at all locations. Vlan 501 to 1841 router number 1... etc, etc.

As Jon stated, vlans 501 - 508 are always up because the Wimax equipment is connected to a trunk port?

B: Yes. Vlan 501-508 are always up on switch 3560G because the wimax equipment is connected to trunk port (g0/5).

When you connect the 1841, is it always connected to the same port, or can that vary?

B: Should be connected always to same port, if it's posible.

Taking  the above into account, we need to figure out how we can get routes  advertised when the router is connected nly as I think (correct me if  I'm wrong) you only use the vlan for when the router is connected and  nothing else. Is that the case?

B: Yep, that is the case. I only use vlan 506 when mobile #6 is connected at one location.

The  vlan is up/up at all times because the wimax equipment is connected to  the port. This switch (3560s?) is advertising its routes via eigrp  always because the vlan is up/up. We need to have some way of  determining when to launch a script. There has to be some event that we  can identify, whether it be a port up event or some log entry that the  script can watch to trigger the script. For example, if you told us that  you always plug the router into fa0/1 on the switch, we could write the  script to advertise the network that you want only when that interface  is seen to come up. In that case, you'd probably want port security  configured on the switch as well to protect the port from coming up  unless it was the router.

This  is going to be next to impossible though if you use the vlan for more  than just this router. For example, if there is other equipment on that  vlan that you have to take into account, you're going to need to  advertise the subnet all the time regardless if the router is connected  or not. Is this the case? If not, is there a way that you could dedicate  a port (if you're not already) to the router at each location?

B: Well, i think that with mine above answers this paragraph is understand, no? I use vlan 501 to 1841 number 1 and so on until 1841 router number 8 with vlan 508. Yes, i can dedicate a port on 3560G switch at wich location on port g0/5.

Respecting to draw i only have one scheme in visio.....

Thanks a lot, guys!

[Bruno Silva]

Meanwhile...

I was wondering if it's not possible to remove eigrp between 7301 central router and 3560G switch... and put static routing, and in the 3560G switch i try to constantly ping the ip of vlan 50X interface of 1841 mobile router, and when receive icmp sucessfully answer, it could add a static route to local subnet of 1841 mobile router on 7301 central router..... all of this with EEM.

kind of consufe.... but if you don´t understand i'll try to explain me again.

Thanks,

Bruno

[Bruno Silva]

The scheme.

https://drive.google.com/file/d/0B2d8xAHjmF2PVGxwTFhQQi1nZ1k/edit?usp=sharing

Bruno

[Jon Marshall]

Bruno

I understand what you are saying but i think the easier solution is to run EEM on the 3560 and not the 7301 (which may not support it anyway).   And the 7301 is your core device so you don't really want to be adding and removing routes on there.

I was rereading John's post and unless i misunderstand i'm not sure a link up will work because the trunk link is up all the time so there won't be link up message on the 3560 when the 1841 is connected to the WiMAX bridge.  How we determine when the 1841 has been connected is still to be decided.  I'm hoping John has some ideas based on your answers.

But whatever triggers the EEM script i think the resulting action should simply be to add a "network " statement to the EIGRP config on the 3560. No need to do anything on the 7301.

Obviously something has to happen when the router is disconnected as well ie. remove the network statement from the EIGRP config on that 3560 so it is no longer advertised to the 7301.

But like i say, i think it's best if we leave the 7301 with the config it has and concentrate on the 3560 switches instead.

Jon