multiple uplinks on a 2801 router

[Whit Hicks]

I need to connect multiple (3 - to start with) DSL modems to a 2801 router.  The router is connected to a point to point bridge with another 2801 on the other end.  Can I route traffic over the bridge and then break it out to a specific DSL uplink port based on Vlan (or is there another way it should be segregated)? Like this:

[Peter Paluch]

Hi Whit,

Even though your two 2801 routers are connected by a point-to-point bridge, I suppose that the 2801 routers themselves are configured for routing, not bridging. In other words, my understanding of your logical IP topology is:

Net 1 (IP subnet 1) \
Net 2 (IP subnet 2) - 2801 --- (IP subnet 4) --- 2801 with DSL routers
Net 3 (IP subnet 3) /

In this case, the 2801 with DSL routers would no longer see any VLANs. However, it will nonetheless see the source IP addresses of packets from Net 1 through Net 3, and use the source IP address to decide what DSL router these packets should be forwarded over. You can use PBR (Policy Based Routing) for that - are you familiar with that feature?

In addition, a 2801 router has only 2 built-in Ethernet ports. How are you going to connect 3 DSL routers to the 2801? Are you going to have them all on a commong network attached to one of the built-in ports on 2801? I assume that the DSL routers are going to operate as full routers, not as DSL modems/bridges.

Best regards,
Peter

[Whit Hicks]

Peter,

The 2801s have 8 port switch cards in them and 4 port VoIP cards.  The DSL modems are set to bridge only.  We need to handle PPPoE on our router.  I am not familiar with PBR, but sounds like where we need to go.  Our plan is to have three user groups (subnets) that have two vlans, one to uplink to the Internet, and the other to route to the a VoIP gateway, for local, and a VoIP trunk for long distance.  We will manage the PBX(s) inside the networks.

[Peter Paluch]

Hi Whit,

Thanks for responding.

The design you are proposing needs additional details to be clarified. You are saying that there are going to be three user groups - subnets. In that case, you will need three VLANs just to contain each user group. I assume that the users will be connected to the 8-port switch cards in the routers, so to keep these three groups separated, you need to enclose each of them into their dedicated VLAN.

Furthermore, the DSL connection will require a standalone VLAN for each DSL modem. The reason is that a PPPoE session is established dynamically, based on broadcasting. If the three DSL modems were all placed in a single "internet uplink" VLAN, a single PPPoE client running on the router would establish its session over any of the three DSL routers, depending on random chance (mostly on network transmission delays), and each time, the DSL router could be different. Even more, running multiple PPPoE clients on the router would not guarantee that each one of them would use a standalone DSL router. It would be possible that all three PPPoE sessions would be handled by the same DSL router, leaving the other two unused. Therefore, it will be necessary to place each DSL modem into its own separate VLAN and run one particular PPPoE client in each VLAN, to make sure there is a 1:1 mapping between PPPoE clients and the DSL modems. You will not be dealing with these dedicated VLANs directly, though, because a PPPoE session is represent by a so-called Dialer interface that is independent of a VLAN.

As a very, very brief and sketchy example, this would be the configuration for the 2811 with the DLS modems (no NAT, no PBR, just a very preliminary example):

vlan 11
 name DSL1
vlan 12
 name DSL2
vlan 13
 name DSL3
!
interface FastEthernet1/0/1
 description => To DSL modem 1 <=
 switchport mode access
 switchport access vlan 11
!
interface FastEthernet1/0/2
 description => To DSL modem 2 <=
 switchport mode access
 switchport access vlan 12
!
interface FastEthernet1/0/3
 description => To DSL modem 3 <=
 switchport mode access
 switchport access vlan 13
!
interface Vlan11
 description => PPPoE client for DSL modem 1 <=
 pppoe-client dial-pool-number 1
 no shutdown
!
interface Vlan12
 description => PPPoE client for DSL modem 2 <=
 pppoe-client dial-pool-number 2
 no shutdown
!
interface Vlan13
 description => PPPoE client for DSL modem 3 <=
 pppoe-client dial-pool-number 3
 no shutdown
!
interface Dialer1
 description => Internet access over DSL modem 1 <=
 mtu 1492
 ip tcp adjust-mss 1452
 ip address negotiated
 encapsulation ppp
 dialer pool 1
!
interface Dialer2
 description => Internet access over DSL modem 2 <=
 mtu 1492
 ip tcp adjust-mss 1452
 ip address negotiated
 encapsulation ppp
 dialer pool 2
!
interface Dialer3
 description => Internet access over DSL modem 3 <=
 mtu 1492
 ip tcp adjust-mss 1452
 ip address negotiated
 encapsulation ppp
 dialer pool 3

In this example, interfaces Dialer1 through Dialer3 would represent the three internet uplinks, and we would use PBR to select traffic based on source IP address (network 1 through network 3) and direct it out a particular Dialer interface.

You have not commented on the nature of the link between the two 2811 routers but I would like to point out that this link will need to operate as a routed link. That means that the VLANs from one router will not span across this link contiguously over to the other 2811. The VLANs will need to be terminated on each router and packets from these VLANs will be routed through the link to the other 2811. This will require either configuring static routing between these two routers, or running a routing protocol so that the routers are aware of the IP networks in the individual VLANs. Please let me know if we agree on these points.

How can I now help you further? In order for me to provide workable configuration examples, I would need to know more about the addressing you intend to deploy, ports you intend to connect, etc. - the implementation details.

Best regards,
Peter

[Whit Hicks]

Peter,

Your points are excellent.

I would expect to give each group its own vlan and subnet for Internet traffic, and a vlan and subnet for VoIP.  I am a little familiar with the dialer, we have been using that protocol with our single network.  So, we would trunk all vlans between the two routers, right?  The "Delta" router would have three connections to three dsl modems.  The "Delta" router would connect to the bridge radio that wirelessly links to another bridge radio and uplinks the "1414" router.  The "1414" router connects to a Firewall for one network, and two other bridges for the other two networks.  "1414" is the hub of the network.  The goal is to back haul three user group back to three separate DSL modems across the same bridge.  I am sure it will require routing on both ends instead of simply layer 2 trunking.

I will attach a diagram so you can see where I am trying to go.

Whit

[Whit Hicks]

Peter,

I just got back to this.  I was considering another way, but this seems to be the best way to connect across my network.  I have configured a 2801 router as shown on the attachment (just as you suggested).  Now I need to bridge it to the other end to another 2801.  I plan to connect the bridge to fastethernet0/0.

I would connect the remote 2801 (I will call it 1414) to the far end of the bridge on fastethernet0/0 as well.  Next I would assume I would need three ports configured for each Vlan 11, 12, and 13 (fastethernet0/1/0, 0/1/1, and 0/1/2), right?  My goal is to have each of these connections act as individual Internet uplinks on the 1414 router.

The big question is how to pass this across the bridge.  I think you mentioned that I will need subnets for each.  I could use 192.168.11.xxx/24, 192.168.12.xxx/24 and 192.168.13.xxx/24, if that works.  The layer 3 stuff is a challenge for me.

Thanks for any help you can lend.

Whit