Dual stack OSPF redistribution in MP-BGP

Question

My topology is working perfectly fine and is as follows:

CE1 <-> PE1 <-> P1 <-> P2 <-> PE2 <-> CE2

• CE1 <-> PE1 and CE2 <-> PE2 are having OSPFv3 with address-family ipv4 and ipv6 both.

• PE1 <-> PE2 is running MP-iBGP with dual-stack support

Redistribution of OSPF in MP-iBGP is as follows:

Config snippet in PE1 & PE2:

address-family ipv6 vrf custA
redistribute connected
redistribute ospf 6
no sync

address-family ipv4 vrf custA
redistribute connected
redistribute ospfv3 6
no sync

CE1 & CE2 are able to reach the IPv4 and IPv6 subnets of each other.

Question:

What is the difference in these two highlighted commands:

In ipv6 address-family it should be redistribute ospf 6 command while in ipv4 address-family it should always be redistribute ospfv3 6. If I interchange these commands within the address-families, both IPv4 & IPv6 networks of CE1 & CE2 become unreachable.

Seems to be a mystery to me. Pl let me know if any other details are required. Any clarification is appreciated.

Answer 1

Only OSPFv3 supports IPv6 (not OSPFv2), so in IPv6 address-family I believe they assume that 'redistribute ospf 6' means you would by default only want OSPFv3 protocol-garnered routes, because that's the only source of them and you're in the family that deals with those routes already.

Contrastly, in IPv4 address family, 'redistribute ospfv3 6' specifically says that the protocol ospfv3 should have it's ipv6 routes redistributed. It's like a reminder that you can only get them from OSPFv3, and not OSPFv2 (though you can get ipv4 routes from OSPFv3, as it was intended to not only support ipv6, but also ipv4 so it could replace OSPFv2).

That's my 'educated guess' anyway :)