CCNP (Cisco Certified Network Professional) Route Certification Exam Cram Notes

3. Layer3 Technologies

3.2 Identify IPv6 addressing and subnetting

IPv6 packet is 128 bits long. It will have basic packet header, and optional extension header.

IPv6 hosts should support the following addresses:

  • Assigned global unicast and anycast addresses (2000::/3)
  • Loopback address (::1/128)
  • Link-local address (FE80::/10), autoconfigured
  • All-nodes multicast addresses (FF01::1 and FF02::1)

1. Unicast site-local addresses - IPv6 unicast site-local addresses are similar to IPv4 private addresses. The scope of a site-local address is the internetwork of an organization's site. (You can use both global addresses and site-local addresses in your network.) The prefix for site-local addresses is FEC0::/48.

2. Unicast unspecified address - The IPv6 unicast unspecified address is equivalent to the IPv4 unspecified address of 0.0.0.0. The IPv6 unspecified address is 0:0:0:0:0:0:0:0:, or a double colon (::).

3. Unicast loopback address - The IPv6 unicast loopback address is equivalent to the IPv4 loopback address, 127.0.0.1. The IPv6 loopback address is 0:0:0:0:0:0:0:1, or ::1

In an IPv6 network, a host can autoconfigure its IP address without the help of a DHCP server.

1. Automatic 6to4 is a point-to-multipoint tunneling method, where the tunnel destination is determined from the border router IPv4 address facing the IPv4 network.

2. The border routers that delimit the 6to4 tunnel must support IPv4 and IPv6 and are not configured in pair.

3. Automatic 6to4 can be used to connect two IPv6 networks as well an IPv6 host to an IPv6 network.

4. IPv6 network is treated as NBMA link.

5. The IPv4 embedded in IPv6 is used to find the other end of the tunnel.

6. Border routers create a tunnel on a per packet basis to other IPv6 Border router.

The following are true about IPv6 address format

1. The total length of IPv6 address is 128 bits

2. The first 48 bits of the IPv6 global unicast address are used for global routing at the Internet Service Provider (ISP) level.

3. 16 bits (after the first 48-bit global unicast address) are used for subnetting, allowing organizations to subdivide their network

4. Multicast addresses are in the range FF00::/8.

5. In an IPv6 network, a host can auto configure its IP address without the help of a DHCP server.

Basic rules:

1. ":" in every 2 bytes.

2. heading 0s in each block can be omitted

3. "0: all zeros in between :0" can be written as "::"

How to map IP Multicast address to MAC address:

The high order 9 bits (out of total of 32 bits) of the IP address are not used for mapping into the MAC address. The lower 23 bits are mapped to lower 23 bits of MAC address.

For example, take a Multicast address: 224.252.6.24. Convert to binary equivalent:224.252.6.24 = 1110.0000.1111.1100.0000.0110.0001.1000

Take only the last 23 bits = 111.1100.0000.0110.0001.1000 = 7C-09-24

Append the Ethernet Multicast address: 01-00-5E. Note that 01-00-5E always precedes a Multicast MAC address. The bit following this is always a zero.

Therefore, Multicast MAC address for IP address 224.252.6.24 is:01-00-5E-7C-09-24.

Note that 01-00-5E-FC-09-18 is NOT correct, since 9th bit needs to be replaced by 0, as explained above.

The EUI-64 format interface ID is derived from the 48-bit MAC address by inserting the hex FFFE between the organizationally unique identifier (OUI) field (the upper three bytes) and the vendor code (the lower three bytes) of the MAC address. The seventh bit in the first byte of the resulting interface ID, corresponding to the Universal/Local (U/L) bit, is set to binary 1.

IPv4 and IPv6 networks can exist simultaneously. It is possible to tunnel IPv6 packets through IPv4 networks. IPv6 is downwards compatible with IPv4.

IPv6 hosts should support the following addresses:

  • Assigned global unicast and anycast addresses (2000::/3)
  • Loopback address (::1/128)
  • Link-local address (FE80::/10), autoconfigured
  • All-nodes multicast addresses (FF01::1 and FF02::1)
  • Solicited-nodes multicast addresses (FF02::1:FF00:/104 and appending the last 24 bits of the corresponding unicast or anycast address of the device)
  • Any other assigned multicast addresses (in the range FF00::/8)

Routers should additionally support at least the following:

  • Subnet-router anycast address
  • All-routers multicast addresses (FF01::2, FF02::2, and FF05::2)
  • The minimum MTU supported in IPv6 is 1280 octets. The recommended MTU value for IPv6 links is 1500 octets.

IPv6 Multicast Addresses used by different routing protocols:

RIPv6 : FF02::9
OSPF speaker: FF02::5
OSPF DR and BDR: FF02::6
Multicast Address Node Local::
FF01:0:0:0:0:0:0:1 or FF01::1 All Nodes Address
FF01:0:0:0:0:0:0:2 or FF01::2 All Routers Address
Link Local:
FF02:0:0:0:0:0:0:1 or FF02::1 All Nodes Address
FF02:0:0:0:0:0:0:2 or FF02::2 All Routers Address
FF02:0:0:0:0:0:0:D or FF02::D All PIM Routers

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