Dual Stack

Dual Stack

Dual Stack is a way to implement IPv6 and still remain compatible with IPv4. A node that runs both IPv6 and IPv6 protocol stacks is called an IPv6/IPv6 node. An IPv6/IPv4 node communicates using IPv6 packets with IPv6 nodes and using IPv4 packets with IPv4 nodes.

Consider the following-

Two IPv6/IPv4 nodes, R5 and R6, are connected to each other via a Fastethernet interface. The Fastethernet interface is configured with an IPv4 as well as an IPv6 address.

The show ip interface brief command shows the interfaces configured with IPv4 addresses on R5.

R5# show ip interface brief

Interface IP-Address OK? Method Status Protocol

FastEthernet0/0 10.1.1.1 YES NVRAM up up

FastEthernet0/1 unassigned YES NVRAM administratively down down

Loopback0 5.5.5.5 YES NVRAM up up

Loopback1 unassigned YES unset up up

The show ipv6 interface brief command shows the interfaces configured with IPv6 addresses on R5.

R5# show ipv6 interface brief

FastEthernet0/0 [up/up]

FE80::C009:10FF:FE38:0

2001::C009:10FF:FE38:0

FastEthernet0/1 [administratively down/down]

Loopback0 [up/up]

Loopback1 [up/up]

FE80::C009:10FF:FE38:0

2002:ABAB::C009:10FF:FE38:0

The show ip route command shows the IPv4 routing table on R5. It shows that Loopback0 interface of R6 is reachable through Fa 0/0.

R5# show ip route | begin Gateway

Gateway of last resort is not set

5.0.0.0/32 is subnetted, 1 subnets

C 5.5.5.5 is directly connected, Loopback0

6.0.0.0/32 is subnetted, 1 subnets

O 6.6.6.6 [110/20] via 10.1.1.2, 00:05:42, FastEthernet0/0

10.0.0.0/30 is subnetted, 1 subnets

C 10.1.1.0 is directly connected, FastEthernet0/0

The show ipv6 route command shows the IPv6 routing table on R5. It shows that the Loopback1 interface of R6 is also reachable through Fastethernet 0/0.

R5# show ipv6 route

IPv6 Routing Table - 7 entries

Codes: C - Connected, L - Local, S - Static, R - RIP, B - BGP

U - Per-user Static route

I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea, IS - ISIS summary

O - OSPF intra, OI - OSPF inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2

ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2

C 2001::/64 [0/0]

via ::, FastEthernet0/0

L 2001::C009:10FF:FE38:0/128 [0/0]

via ::, FastEthernet0/0

C 2002:ABAB::/64 [0/0]

via ::, Loopback1

L 2002:ABAB::C009:10FF:FE38:0/128 [0/0]

via ::, Loopback1

R 2003:ABAB::/64 [120/2]

via FE80::C00A:17FF:FE04:0, FastEthernet0/0

L FE80::/10 [0/0]

via ::, Null0

L FF00::/8 [0/0]

via ::, Null0

The following output shows IPv4 traffic flowing from R5 to R6 through outgoing interface Fastethernet 0/0.

The following output shows IPv6 traffic flowing from R6 to R5 through outgoing Fastethernet 0/0.