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Configure the switch layer 3 port connected to a firewall

Hello,

I  would like a help about a configuration, so I have a switch layer 6500  series connected to a firewall, the port configuration between them is  layer 2, in another words I do not configure an IP address in the Cisco  switch port to conected it in the firewall, but when a apply a policy on  firewall it lose communication with others vlans, just the vlan that is  connected between the switch and firewall works, attachment the design.  I think that is necessary to configure the connection between the  firewall and switch as layer 3 ( a port with IP address in the switch),  but I would like to know why? The switch is configured with about 10  vlan and it is a inter vlan routing, a default route is configured in  the switch where the gateway is the firewall.

Note: The comments in the picture attachment is in portugues, but nothing important.

1 ACCEPTED SOLUTION

Accepted Solutions
Hall of Fame Super Blue

Re: Configure the switch layer 3 port connected to a firewall

Alexander

Difficult to say without seeing config. Here are your 2 options in more detail -

1) use a L2 port. So lets say the L2 port is in vlan 10 and the subnet is 192.168.5.0/24

6500 end

======

int vlan 10

ip address 192.168.5.1 255.255.255.0

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Firewall interface connecting to 6500 would be given an IP of 192.168.5.1 (the 6500 vlan 10 ip). Then on the firewall for each other vlan subnet on the 6500 you would need to add routes for those subnets eg.

ip route 192.168.6.0 255.255.255.0 192.168.5.1  <-- where 192.168.6.0/24 is a different vlan/subnet on the 6500.

2) If you use a L3 port then

6500 end

=======

int gi0/1  <-- connects to firewall

no switchport

ip address 192.168.5.1 255.255.255.252  <-- note you only need a /30 subnet for a P2P routed link

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Again, the firewall interface connecting to the 6500 is given 192.168.5.2 255.255.255.252. You then need to add routes to the firewall as in previous example except this time you also need to add a route for the server vlan as well.

One last point. I have used the example of adding static routes to the firewall but you could, if supported, use a dynamic routing protocol on your firewall and 6500 to exchange the 6500 subnets.

Jon

6 REPLIES
Hall of Fame Super Blue

Configure the switch layer 3 port connected to a firewall

Alexander

Shouldn't matter whether you use L2 port or L3 port, both should work. But if you use L2 port obviously you  need a L3 valn interface for that vlan on the 6500 for the firewall to communicate with the other vlans.

Perhaps it is your firewall policy that is the problem.

Jon

New Member

Configure the switch layer 3 port connected to a firewall

Jon,

but when a apply a policy on firewall all the other vlans stops to works properly, it did not connect to Internet, just the vlan where the servers stay works and the connection between the firewall and 6500 switch is in this default vlan(server vlan), with the SVI configurated. So I think if I configure a L3 route port in the Cisco switch where the firewall connect should works, because all vlan will be routed, but I would like to make sure about that.

Hall of Fame Super Blue

Re: Configure the switch layer 3 port connected to a firewall

Alexander

Difficult to say without seeing config. Here are your 2 options in more detail -

1) use a L2 port. So lets say the L2 port is in vlan 10 and the subnet is 192.168.5.0/24

6500 end

======

int vlan 10

ip address 192.168.5.1 255.255.255.0

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Firewall interface connecting to 6500 would be given an IP of 192.168.5.1 (the 6500 vlan 10 ip). Then on the firewall for each other vlan subnet on the 6500 you would need to add routes for those subnets eg.

ip route 192.168.6.0 255.255.255.0 192.168.5.1  <-- where 192.168.6.0/24 is a different vlan/subnet on the 6500.

2) If you use a L3 port then

6500 end

=======

int gi0/1  <-- connects to firewall

no switchport

ip address 192.168.5.1 255.255.255.252  <-- note you only need a /30 subnet for a P2P routed link

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Again, the firewall interface connecting to the 6500 is given 192.168.5.2 255.255.255.252. You then need to add routes to the firewall as in previous example except this time you also need to add a route for the server vlan as well.

One last point. I have used the example of adding static routes to the firewall but you could, if supported, use a dynamic routing protocol on your firewall and 6500 to exchange the 6500 subnets.

Jon

New Member

Configure the switch layer 3 port connected to a firewall

Jon,

First of all thank you for your help. But...

1) use a L2 port. So lets say the L2 port is in vlan 10 and the subnet is 192.168.5.0/24

6500 end

======

int vlan 10

ip address 192.168.5.1 255.255.255.0

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Firewall  interface connecting to 6500 would be given an IP of 192.168.5.1 (the  6500 vlan 10 ip). Then on the firewall for each other vlan subnet on the  6500 you would need to add routes for those subnets eg.

ip route 192.168.6.0 255.255.255.0 192.168.5.1  <-- where 192.168.6.0/24 is a different vlan/subnet on the 6500.

Where you said

"Firewall  interface connecting to 6500 would be given an IP of 192.168.5.1 (the  6500 vlan 10 ip)"

And

"

int vlan 10

ip address 192.168.5.1 255.255.255.0

"

So... Do you need to put the same ip address on firewall interface and in the switch vlan(192.168.5.1)"?

And the route

ip route 0.0.0.0 0.0.0.0 192.168.5.2

Who is 192.168.5.2?

Hall of Fame Super Blue

Configure the switch layer 3 port connected to a firewall

Alexander

No, the 6500 would use 192.168.5.1 on the vlan 10 interface. The firewall interface connected to the 6500 would use 192.168.5.2. They can't use the same IP.

so "ip route 0.0.0.0 0.0.0.0 192.168.5.2" on the 6500 says sends all traffic for unknown destinations (usually internet traffic) to the firewall interface.

Jon

New Member

Re: Configure the switch layer 3 port connected to a firewall

Hi Jon Marshall,
I do not understand the below sentence:
"except this time you also need to add a route for the server vlan as well."
which does the server vlan in this case?
Thanks a lot.

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