ipv6 multicast address and ethernet destination address

[sarahr202]

Hi everybody.

When router sends an ipv6 packet at ipv6 multicast address, what  destination address does router use in ethernet header?

For example below is the captured packet sent by router at multicast address ff02::1:ff98:0, I found router is using 33:33:ff:98:00:00 as destination address in ethernet header as shown below:

My question will router always use this ethernet destination address for ipv6 packets destined at multicast address?

No.     Time        Source                Destination           Protocol Length Info

      2 0.297000    ::                    ff02::1:ff98:0        ICMPv6   78     Neighbor Solicitation for fe80::c200:cff:fe98:0

Frame 2: 78 bytes on wire (624 bits), 78 bytes captured (624 bits)

Ethernet II, Src: c0:00:0c:98:00:00 (c0:00:0c:98:00:00), Dst: IPv6mcast_ff:98:00:00 (33:33:ff:98:00:00)

    Destination: IPv6mcast_ff:98:00:00 (33:33:ff:98:00:00)

    Source: c0:00:0c:98:00:00 (c0:00:0c:98:00:00)

    Type: IPv6 (0x86dd)

Internet Protocol Version 6, Src: :: (::), Dst: ff02::1:ff98:0 (ff02::1:ff98:0)

Internet Control Message Protocol v6

Thanks and have a great day.

[lgijssel · Accepted solution]

Hi there,

You seem to have a lot of questions regarding ipv6. Are you aware that there is a dedicated forum for this?

Perhaps useful for your next posting, if any.

Anyway, the answer to your question can be bound in the following link: (page 6)

http://www.cisco.com/en/US/prod/collateral/iosswrel/ps6537/ps6552/ps6594/product_data_sheet0900aecd80320fb8.pdf

regards,

Leo

[sarahr202]

Thanks Leo.

The link indeed answers my question but not all the questions  that I have. Would you be kind enough to direct me to some link that can?.

For example;

1)  I observed on ethernet interface, router advertises link prefix and  if a host is configured for auto ipv6 addressing, host can configure itself.  Now if I have two routers connected via serial link, one of them say r2 is configured for ipv6 auto addressing, will this router configure its ipv6 address upon receipt of prefix in " ROUTER ADVERTISEMENT" ?

2) On Ethernet, I observed an ipv6-enabled host first perform DAD on its local link address, if no response is heard, it announces its corresponding mac address.  Same process is followed for globally unicast ipv6 address. The question should we expect the same behavior on serial interface ?

Thanks and have a great day.

[lgijssel · Accepted solution]

Your questions are skimming the edge of relevance but nevertheless I will attempt to provide a suitable answer.

One thing is, there is a fundamental difference between an autoconfigured system and a router.

According to the standard, routers are required to announce their presence on the network.

This is mainly to enable other hosts to perform automatic configuration.

One of the consequences of making a router perform autoconfig is that it will behave as any other host on the network but not as a router anymore(!). When you set this up in a lab like I have done, you will probably see what I mean.

The other thing is that there are fundamental differences between ethernet (Broadcast, MultiAccess) and serial lines which are typically non-broadcast point-point. What purpose would it serve to have an autoconfigured ipv6 host at one end of a serial line and a router at the other? The standard solution would be to use a router and connect the host to an ethernet interface of that router.

One more useful link:

http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_7-2/ipv6_autoconfig.html

regards,

Leo

[sarahr202]

Thanks Leo.