IPv6 OSPFv3 Default Route

(Rene Molenaar) #1

This topic is to discuss the following lesson:

(Rene Molenaar) #2

Why do you have to activate OSPF on the interface? You don’t have to do this for IPv4.

(Lazaros Agapides) #3

This question was originally posted by @maxturpin, I’m not sure why it has changed ownership. However, I will answer the question here.

OSPFv3 has a different philosophy than OSPFv2 for IPv4. In IPv4, OSPF is enabled globally and the participating networks are added using the network command. OSPFv3 functions differently. You enable OSPF on the participating interface. in this way, you are indicating which subnets are participating (the subnet directly connected to the interface) and you are also indicating the area to which the interface belongs. This is more intuitive than the configuration method of OSPFv2 because OSPF configuration is inherently connected to interfaces. Both types of logic work, however, OSPFv3 seems a bit more elegant. It is also easier to implement since you don’t have to think about what subnets you will include, but what interfaces will participate.

I hope this has been helpful!


(Vinod A) #4

Hi Rene,
What is signfinace of TAG value …I see it get changes in examples . For example ,in your document it is 1 and in my example it is 100

R1#sh ipv6 route
IPv6 Routing Table - default - 4 entries
Codes: C - Connected, L - Local, S - Static, U - Per-user Static route
       B - BGP, HA - Home Agent, MR - Mobile Router, R - RIP
       H - NHRP, I1 - ISIS L1, I2 - ISIS L2, IA - ISIS interarea
       IS - ISIS summary, D - EIGRP, EX - EIGRP external, NM - NEMO
       ND - ND Default, NDp - ND Prefix, DCE - Destination, NDr - Redirect
       O - OSPF Intra, OI - OSPF Inter, OE1 - OSPF ext 1, OE2 - OSPF ext 2
       ON1 - OSPF NSSA ext 1, ON2 - OSPF NSSA ext 2, l - LISP
OE2 ::/0 [110/1], **tag 100**
     via FE80::A8BB:CCFF:FE00:100, Ethernet0/0
C   2001:DB8:12:12::/64 [0/0]
     via Ethernet0/0, directly connected
L   2001:DB8:12:12::1/128 [0/0]
     via Ethernet0/0, receive
L   FF00::/8 [0/0]
     via Null0, receive

(Rene Molenaar) #5

Hi Vinod,

Good question, I never really noticed it before. The answer is in the RFC:


Inclusion of a forwarding address or external route tag in AS-external-LSAs is now optional. In addition, AS-external-LSAs can now reference another LSA, for inclusion of additional route attributes that are outside the scope of the OSPF protocol. For example, this reference could be used to attach BGP path attributes to external routes.

The external route tag is present in the AS-external-LSA if and only if the AS-external-LSA’s bit T is set.

Seems they decided to add a route tag by default for OSPFv3 external routes. We use these tags in redistribution: