Accepted Solutions
Hi Josh,
I apologize for responding so late - these have been busy days.
Let me try to provide you with a simple example of configurations for three routers that use tunneling to transport IPv4 and IPv6 packets - you can then compare your configurations with the ones provided here.
In this topology, it is assumed that R2 does not run IPv6 at all, and in addition, R2 knows only the directly connected networks, and has no idea about the private networks 10.0.1.0/24 and 10.0.2.0/24 behind R1 and R3, respectively. In order to allow the networks behind R1 and R3 to talk to each other, a tunnel needs to be established between R1 and R3, and routing run over it.
R2's configuration, as far as IP is concerned, will be extremely simple:
hostname R2 ! interface FastEthernet0/0 description => To R1 <= ip address 192.0.2.2 255.255.255.252 no shutdown ! interface FastEthernet0/1 description => To R3 <= ip address 192.0.2.5 255.255.255.252 no shutdown
Basic R1 configuration (no tunnel yet) will also be relatively simple:
hostname R1 ! ipv6 unicast-routing ipv6 cef ! interface FastEthernet0/0 description => To R2 <= ip address 192.0.2.1 255.255.255.252 no shutdown ! interface FastEthernet1/0 description => IPv4 LAN <= ip address 10.0.1.1 255.255.255.0 no shutdown ! interface FastEthernet1/1 description => IPv6 LAN <= ipv6 address 2001:db8:cafe:1::1/64 no shutdown ! ip route 0.0.0.0 0.0.0.0 192.0.2.2
R3's configuration would be very similar:
hostname R3 ! ipv6 unicast-routing ipv6 cef ! interface FastEthernet0/1 description => To R2 <= ip address 192.0.2.6 255.255.255.252 no shutdown ! interface FastEthernet1/0 description => IPv4 LAN <= ip address 10.0.2.1 255.255.255.0 no shutdown ! interface FastEthernet1/1 description => IPv6 LAN <= ipv6 address 2001:db8:cafe:2::1/64 no shutdown ! ip route 0.0.0.0 0.0.0.0 192.0.2.5
At this point, R3 would be able to ping R1 (and vice versa) using their public addresses, but hosts in the private IPv4 LANs would be unable to talk to each other, not even talking about the IPv6 LANs.
The most straightforward tunneling configuration here would be to create a GRE tunnel that is capable of tunneling both IPv4 and IPv6 at the same time, and have R1 and R3 advertise their networks over this tunnel.
On R1, you would add the following configuration:
interface Tunnel0 description => GRE tunnel to R3 <= tunnel source 192.0.2.1 tunnel destination 192.0.2.6 ip address 10.0.13.1 255.255.255.0 ipv6 enable ip ospf 1 area 0 ipv6 ospf 1 area 0 ! interface FastEthernet1/0 ip ospf 1 area 0 ! interface FastEthernet1/1 ipv6 ospf 1 area 0
R3's configuration would be again similar:
interface Tunnel0 description => GRE tunnel to R1 <= tunnel source 192.0.2.6 tunnel destination 192.0.2.1 ip address 10.0.13.2 255.255.255.0 ipv6 enable ip ospf 1 area 0 ipv6 ospf 1 area 0 ! interface FastEthernet1/0 ip ospf 1 area 0 ! interface FastEthernet1/1 ipv6 ospf 1 area 0
This configuration would set up a static GRE tunnel between R1 and R3 and run both OSPFv2 (IPv4) and OSPFv3 (IPv6) over this tunnel, enabling R1 and R3 learn about their networks through this tunnel and pass packets from these networks through this tunnel.
The tunnel itself, as an interface, is assigned an IPv4 and IPv6 address on both R1 and R3. This is necessary for two purposes: First, an interface without an assigned IPv4 (IPv6) address is not considered an interface enabled for IPv4 (IPv6), and no IPv4 (IPv6) packets are allowed to pass through it. Second, routing protocols and other mechanisms running on the router that originate IP packets require that each interface of the router has an IPv4 (IPv6) address assigned, otherwise a packet originated by the router and sent out a particular interface would not have any source IPv4 (IPv6) address. For example, the OSPFv2 packets originated by R1 and sent out the Tunnel0 interface will have their source IPv4 address set to 10.0.13.1. Of course you have to keep in mind that there is always tunneling involved, so the entire OSPFv2 packet sent by R1 will be:
Outer header (S=192.0.2.1, D=192.0.2.6) | GRE | Inner header (S=10.0.13.1, D=224.0.0.5)
Now, for IPv4, I have assigned explicit IPv4 addresses to the tunnel interfaces. For IPv6, I've made a little trick: Because the tunnel is a purely transit link, most probably not intended to be "pinged" from any remote location, I have simply used the ipv6 enable command on both tunnel interfaces which will cause the router to create link-local unicast addresses for the interfaces and start the IPv6 on the interfaces. These tunnel interface won't have any global unicast IPv6 addresses assigned because for the basic operation, they do not need them. Of course I could assign global IPv6 addresses to the tunnel interfaces, but in this topology, it would not be useful: OSPFv3, just like any internal IPv6 routing protocol, uses only link-local addresses as next hop addresses, and the global addresses would be irrelevant as far as routing is concerned.
Note here that I have used the GRE type of tunnel (it is the default tunnel type). I could have used the IPv6-over-IPv4 tunnel type (tunnel mode ipv6ip) but if I did that, this tunnel would be capable of carrying IPv6 traffic only. That would mean that I would be unable to run OSPFv2 through it, and the 10.0.1.0/24 and 10.0.2.0/24 networks would not be able to operate with it. Only IPv6 packets would be allowed to pass through it. I would in fact need to establish another standalone tunnel for the IPv4 traffic. GRE is much more flexible in this regard, at the expense of extra 4B required for each tunneled packet for its own header.
Please try to go over this carefully. All your questions are welcome.
Best regards,
Peter
Hi Josh,
I apologize for responding so late - these have been busy days.
Let me try to provide you with a simple example of configurations for three routers that use tunneling to transport IPv4 and IPv6 packets - you can then compare your configurations with the ones provided here.
In this topology, it is assumed that R2 does not run IPv6 at all, and in addition, R2 knows only the directly connected networks, and has no idea about the private networks 10.0.1.0/24 and 10.0.2.0/24 behind R1 and R3, respectively. In order to allow the networks behind R1 and R3 to talk to each other, a tunnel needs to be established between R1 and R3, and routing run over it.
R2's configuration, as far as IP is concerned, will be extremely simple:
hostname R2 ! interface FastEthernet0/0 description => To R1 <= ip address 192.0.2.2 255.255.255.252 no shutdown ! interface FastEthernet0/1 description => To R3 <= ip address 192.0.2.5 255.255.255.252 no shutdown
Basic R1 configuration (no tunnel yet) will also be relatively simple:
hostname R1 ! ipv6 unicast-routing ipv6 cef ! interface FastEthernet0/0 description => To R2 <= ip address 192.0.2.1 255.255.255.252 no shutdown ! interface FastEthernet1/0 description => IPv4 LAN <= ip address 10.0.1.1 255.255.255.0 no shutdown ! interface FastEthernet1/1 description => IPv6 LAN <= ipv6 address 2001:db8:cafe:1::1/64 no shutdown ! ip route 0.0.0.0 0.0.0.0 192.0.2.2
R3's configuration would be very similar:
hostname R3 ! ipv6 unicast-routing ipv6 cef ! interface FastEthernet0/1 description => To R2 <= ip address 192.0.2.6 255.255.255.252 no shutdown ! interface FastEthernet1/0 description => IPv4 LAN <= ip address 10.0.2.1 255.255.255.0 no shutdown ! interface FastEthernet1/1 description => IPv6 LAN <= ipv6 address 2001:db8:cafe:2::1/64 no shutdown ! ip route 0.0.0.0 0.0.0.0 192.0.2.5
At this point, R3 would be able to ping R1 (and vice versa) using their public addresses, but hosts in the private IPv4 LANs would be unable to talk to each other, not even talking about the IPv6 LANs.
The most straightforward tunneling configuration here would be to create a GRE tunnel that is capable of tunneling both IPv4 and IPv6 at the same time, and have R1 and R3 advertise their networks over this tunnel.
On R1, you would add the following configuration:
interface Tunnel0 description => GRE tunnel to R3 <= tunnel source 192.0.2.1 tunnel destination 192.0.2.6 ip address 10.0.13.1 255.255.255.0 ipv6 enable ip ospf 1 area 0 ipv6 ospf 1 area 0 ! interface FastEthernet1/0 ip ospf 1 area 0 ! interface FastEthernet1/1 ipv6 ospf 1 area 0
R3's configuration would be again similar:
interface Tunnel0 description => GRE tunnel to R1 <= tunnel source 192.0.2.6 tunnel destination 192.0.2.1 ip address 10.0.13.2 255.255.255.0 ipv6 enable ip ospf 1 area 0 ipv6 ospf 1 area 0 ! interface FastEthernet1/0 ip ospf 1 area 0 ! interface FastEthernet1/1 ipv6 ospf 1 area 0
This configuration would set up a static GRE tunnel between R1 and R3 and run both OSPFv2 (IPv4) and OSPFv3 (IPv6) over this tunnel, enabling R1 and R3 learn about their networks through this tunnel and pass packets from these networks through this tunnel.
The tunnel itself, as an interface, is assigned an IPv4 and IPv6 address on both R1 and R3. This is necessary for two purposes: First, an interface without an assigned IPv4 (IPv6) address is not considered an interface enabled for IPv4 (IPv6), and no IPv4 (IPv6) packets are allowed to pass through it. Second, routing protocols and other mechanisms running on the router that originate IP packets require that each interface of the router has an IPv4 (IPv6) address assigned, otherwise a packet originated by the router and sent out a particular interface would not have any source IPv4 (IPv6) address. For example, the OSPFv2 packets originated by R1 and sent out the Tunnel0 interface will have their source IPv4 address set to 10.0.13.1. Of course you have to keep in mind that there is always tunneling involved, so the entire OSPFv2 packet sent by R1 will be:
Outer header (S=192.0.2.1, D=192.0.2.6) | GRE | Inner header (S=10.0.13.1, D=224.0.0.5)
Now, for IPv4, I have assigned explicit IPv4 addresses to the tunnel interfaces. For IPv6, I've made a little trick: Because the tunnel is a purely transit link, most probably not intended to be "pinged" from any remote location, I have simply used the ipv6 enable command on both tunnel interfaces which will cause the router to create link-local unicast addresses for the interfaces and start the IPv6 on the interfaces. These tunnel interface won't have any global unicast IPv6 addresses assigned because for the basic operation, they do not need them. Of course I could assign global IPv6 addresses to the tunnel interfaces, but in this topology, it would not be useful: OSPFv3, just like any internal IPv6 routing protocol, uses only link-local addresses as next hop addresses, and the global addresses would be irrelevant as far as routing is concerned.
Note here that I have used the GRE type of tunnel (it is the default tunnel type). I could have used the IPv6-over-IPv4 tunnel type (tunnel mode ipv6ip) but if I did that, this tunnel would be capable of carrying IPv6 traffic only. That would mean that I would be unable to run OSPFv2 through it, and the 10.0.1.0/24 and 10.0.2.0/24 networks would not be able to operate with it. Only IPv6 packets would be allowed to pass through it. I would in fact need to establish another standalone tunnel for the IPv4 traffic. GRE is much more flexible in this regard, at the expense of extra 4B required for each tunneled packet for its own header.
Please try to go over this carefully. All your questions are welcome.
Best regards,
Peter
