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Configuring the Catalyst 6500 Switch for IPS Inline Operation of the IDSM

Answered Question
Dec 9th, 2005
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I understand how to configure the Catalyst 6500 switch so that the monitoring ports are access ports in two separate VLAN's for inline operation.


However, I don't see any documentation that describes how the desired VLAN traffic gets forced through the IPS.


In promiscuous mode, you can use VACL's to copy/capture and forward the desired traffic to the IDSM for analysis. I'm not seeing how to get the desired traffic through the IPS.


Note that the host 6500 is running native IOS 12.2(18)SXE.


Thanks for any assistance.

Correct Answer by marcabal about 11 years 8 months ago

A tranparent firewall is a fairly good comparison.


Let's say you have vlan 10 with 100 PCs and 1 Router for the network.

If you want to apply a transparent firewall on that vlan you can not simply put one interface of the firewall on vlan 10. Nothing would go through the firewall.


Instead you have to create a new vlan, let's say 1010. Now you place one interface of the firewall on vlan 10 and the other on vlan 1010. Still nothing is going through the firewall. So now you move that Router from vlan 10 to vlan 1010. All you do is change the vlan, the IP Address and netmask of the router stay the same.

The transparent firewall bridges vlan 10 and vlan 1010. The PCs on vlan 10 ae still able to communicate to and through the router, but must go through the transparent firewall to do so.


The firewall is transparent because it does not IP Route between 2 vlans, instead the same IP subnet exists on both vlans and the firewall transparently beidges traffic between the 2 vlans.


The transparent firewall can do firewalling between the PCs on vlan 10 and the Router on vlan 1010. But is PC A on vlan 10 talks to PC B on vlan 10, then the transparent firewall does not see and can not block that traffic.


An InLine sensor is very similar to the transparent firewall and will bridge between the 2 vlans. And similarly an InLine sensor is able to InLine monitor traffic between PCs on vlan 10 and the Router on vlan 1010, but will not be able to monitor traffic between 2 PCs on vlan 10.


Now the router on one vlan and the PCs on the other vlan is a typical deployment for inline sensors, but your vlans do not Have to be divided that way. You could choose to place some servers in one vlan, and desktop PCs in the other vlan. You subdivide the vlans in what ever method makes sense for your deployment.


Now for monitoring multiple vlans the same principle still applies. You can't monitor traffic between machines on the same vlan. So for each of the vlans you want to monitor you will need to create a new vlan and split the machines between the 2 vlans.


In your case with Native IOS you are limited to only 1 pair of vlans for InLine monitoring, but your desired deployment would require 20 vlan pairs.

The 5.1 IPS software has now the capability to handle the 20 pairs, but the Native IOS software does not have the capability to send the 40 vlans (20 pairs) to the IDSM-2.


The Native IOS changes are in testing right now, but I have not heard a release date for those changes.


Now Cat OS has already made these changes. So here is a basic breakdown of what you could do in Cat OS and you can use in preparation for a Native IOS deployment when it gets released.


For vlans 10-20, and 300-310 that you want monitored you will need to break each of those vlans in to 2 vlans.

Let's say we make it simple and add 500 to each vlan in order to create the new vlan for each pair.

So you have the following pairs:

10/510, 11/511, 12/512, etc...

300/800, 301/801, 302/802, etc....


You set up the sensor port to trunk all 40 vlans:

set trunk 5/7 10-20,300-310,510-520,800-810

(Then clear all other vlans off that trunk to keep things clean)


In the IDSM-2 configuration create the 20 inline vlan pairs on interface GigabitEthernet0/7


Nw on each of the 20 original vlans move the default router for each vlan from the original vlan to the 500+ vlan.


At this point you should ordinarily be good to go. The IDSM-2 won't be monitoring traffic that stays within each of the original 20 vlans, but Would monitor traffic getting routed in and out of each of the 20 vlans.


Because of a switch bug you may have to have an additional PC moved to the same vlan as the router if the switch/MSFC is being used as the router and you are deploying with an IDSM-2.

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marcabal Sat, 12/10/2005 - 17:42
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Traffic being sent from one vlan through the IDSM-2 to the second vlan simply relies on spanning-tree.


When spanning-tree runs it looks for all paths between switches (or in this case a path between 2 vlans on the same switch).

It checks to see if more than one path exists to another switch (or vlan in this case).

If more than one path exists, then it will place one path in Forwarding state, and the other paths in a Blocking state.


So long as the IDSM-2 ports are the only path between the 2 vlans (or if there are multiple paths then the IDSM-2 is marked for Forwarding), then any packets from a machine in vlan A on one side of the IDSM-2 will have to go through the IDSM-2 to get to any machine in vlan B on the other side of the IDMS-2.

(NOTE: If 2 machines on the same vlan talk to each other, then the packets will not go through the IDSM-2.)


A common scenario would be to place your internal machines on one vlan and your firewall on a second vlan. Then use the IDSM-2 to connect the 2 vlans. So all traffic between the internal network and the Internet has to go through both the firewall and the IDSM-2.


The 2 vlans on the 2 sides of the IDSM-2 should have the same IP subnet. The IDSM-2 does not IP route between the 2 vlans. The IDSM-2 could be considered to bridge the 2 networks.


An easy method for deploying in an existing network is to take an existing vlan with multiple machines. Create one new vlan.

Use the IDSM-2 to connect the 2 vlans.

Initially there will be little to no traffic between the vlans, because there are no machines on one side the IDSM-2.

Now divide the existing vlan into 2 groups of machines. (One method would be to group external connectivity devices like routers and firewalls together, and group personal pc or servers into a second group)

Leave one group in the original vlan.

Move the machines in the other group to the other vlan.


jeff-krauss Mon, 12/12/2005 - 13:09
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Marco,


As always, thank you for the response. I think I catch most of that. However, in an existing network, where we have IDSM's in core 6500's at multiple sites, and have about 60 VLAN's, how do I determine which VLAN's go through the IPSM?


In my scenario, if let’s say one of our core Cat 6500 has VLAN’s 1, 10-30, 60-90, 100,200, and 300-330. I only want to send traffic from VLAN’s 10-20 and 300-310 through the IPS. How do I configure the Switch to send the traffic from the desired VLAN’s through the IPS?


It is my understanding, that right now (on Native IOS), we're limited to only two VLAN's and bridging between those similar to a transparent firewall.


Is the solution to my issue to employ Inline VLAN's (VLAN on a stick)? If so, in what version of Cat 6500 IOS is this anticipated and when approximately (not asking for anything official), do you expect this will be available?


Thanks,


Jeff






Correct Answer
marcabal Mon, 12/12/2005 - 15:51
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  • Cisco Employee,

A tranparent firewall is a fairly good comparison.


Let's say you have vlan 10 with 100 PCs and 1 Router for the network.

If you want to apply a transparent firewall on that vlan you can not simply put one interface of the firewall on vlan 10. Nothing would go through the firewall.


Instead you have to create a new vlan, let's say 1010. Now you place one interface of the firewall on vlan 10 and the other on vlan 1010. Still nothing is going through the firewall. So now you move that Router from vlan 10 to vlan 1010. All you do is change the vlan, the IP Address and netmask of the router stay the same.

The transparent firewall bridges vlan 10 and vlan 1010. The PCs on vlan 10 ae still able to communicate to and through the router, but must go through the transparent firewall to do so.


The firewall is transparent because it does not IP Route between 2 vlans, instead the same IP subnet exists on both vlans and the firewall transparently beidges traffic between the 2 vlans.


The transparent firewall can do firewalling between the PCs on vlan 10 and the Router on vlan 1010. But is PC A on vlan 10 talks to PC B on vlan 10, then the transparent firewall does not see and can not block that traffic.


An InLine sensor is very similar to the transparent firewall and will bridge between the 2 vlans. And similarly an InLine sensor is able to InLine monitor traffic between PCs on vlan 10 and the Router on vlan 1010, but will not be able to monitor traffic between 2 PCs on vlan 10.


Now the router on one vlan and the PCs on the other vlan is a typical deployment for inline sensors, but your vlans do not Have to be divided that way. You could choose to place some servers in one vlan, and desktop PCs in the other vlan. You subdivide the vlans in what ever method makes sense for your deployment.


Now for monitoring multiple vlans the same principle still applies. You can't monitor traffic between machines on the same vlan. So for each of the vlans you want to monitor you will need to create a new vlan and split the machines between the 2 vlans.


In your case with Native IOS you are limited to only 1 pair of vlans for InLine monitoring, but your desired deployment would require 20 vlan pairs.

The 5.1 IPS software has now the capability to handle the 20 pairs, but the Native IOS software does not have the capability to send the 40 vlans (20 pairs) to the IDSM-2.


The Native IOS changes are in testing right now, but I have not heard a release date for those changes.


Now Cat OS has already made these changes. So here is a basic breakdown of what you could do in Cat OS and you can use in preparation for a Native IOS deployment when it gets released.


For vlans 10-20, and 300-310 that you want monitored you will need to break each of those vlans in to 2 vlans.

Let's say we make it simple and add 500 to each vlan in order to create the new vlan for each pair.

So you have the following pairs:

10/510, 11/511, 12/512, etc...

300/800, 301/801, 302/802, etc....


You set up the sensor port to trunk all 40 vlans:

set trunk 5/7 10-20,300-310,510-520,800-810

(Then clear all other vlans off that trunk to keep things clean)


In the IDSM-2 configuration create the 20 inline vlan pairs on interface GigabitEthernet0/7


Nw on each of the 20 original vlans move the default router for each vlan from the original vlan to the 500+ vlan.


At this point you should ordinarily be good to go. The IDSM-2 won't be monitoring traffic that stays within each of the original 20 vlans, but Would monitor traffic getting routed in and out of each of the 20 vlans.


Because of a switch bug you may have to have an additional PC moved to the same vlan as the router if the switch/MSFC is being used as the router and you are deploying with an IDSM-2.

jeff-krauss Tue, 12/13/2005 - 06:28
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Thanks. They should explain that in the documentation!


So, the new VLAN-on-a-stick method (Inline VLAN Pair) in 5.1 is essentially the same as the the current method (Inline Interface) except that it scales by creating each pair on a subinterface?



What is the ID of the switch bug you mention? This is a MLS deployment, so if we're protecting 60 VLAN's, adding an additional 60 PC's just to get the SVI to come up is probably not practical....although I guess you could make the argument that you don't really have to add 60 PC's - you just leave 60 PC's unprotected by putting them on the SVI side of the sensor.



jeff-krauss Thu, 05/04/2006 - 09:34
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Marco,


Any update on release of Native IOS support for inline VLAN pairs on the IDSM-2?


Thanks,


Jeff

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