All Cisco-Network Study Notes: Stateless Agreement with Router Advertisement

Stateless Agreement with Router Advertisement

IPv6 has a stateless agreement approach to accomplish the end node’s agreement easier

(especially with adaptable nodes). It’s alleged stateless because it does not act like DHCP,

where there’s an absolute four-step agreement barter amid the DHCP applicant and the

DHCP server.

Router

IP: 2001:DB8::4

MAC

0000.BEEF.0000

Host C

IP: 2001:DB8::3

MAC

0000.0666.0000

Host B

IP: 2001:DB8::2

MAC

0000.C5C0.0000

Host A

IP: 2001:DB8::1

MAC

0000.CAFE.0000

C5C0 - > CAFE

2001:DB8::2 is at C5C0

128 Chapter 7: Exploiting IPv6 Neighbor Discovery and Router Advertisement

DHCP Four-Step Protocol

DHCP consists of four altered accomplish as declared in Chapter 5:

Step 1 The end bulge sends a advertisement DHCP DISCOVER bulletin and hopes

to ability at atomic one DHCP server.

Step 2 All DHCP servers acknowledgment with a DHCP OFFER bulletin to the end node.

(This packet contains all the agreement information: busy IP

address, subnet mask, aperture address, DNS address, and so on.) The

DHCP servers additionally abundance a state—that is, they abundance the offered busy IP

address on a nonvolatile storage.

Step 3 The end bulge selects one of the DHCP OFFER, at its will and requests

this specific IP abode with a DHCP REQUEST bulletin that’s beatific to

all DHCP servers.

Step 4 Upon cancellation of this request, the DHCP servers either abandon the accompaniment if

the end bulge did not baddest them, or they accumulate the accompaniment about the leased

IP abode if they were selected. The called DHCP server sends a final

DHCP ACK bulletin to the end node.

With this four-step agreement and the use of a accompaniment in the server, DHCP is not so simple.

Hence, there is a charge for a basal stateless (no stored accompaniment about busy address) protocol

for IPv6.

With the stateless configuration, routers periodically (or on request) multicast Router

Advertisements (RA) (transported over ICMPv6). Those RAs back abundant information

for the basal arrangement agreement of an end node. They accommodate the following:

• Bounded prefix(es). First 64 $.25 of the IPv6 address

• Router link-layer address. Abode of the transmitting router

• Associated lifetime. Detects reachability of the transmitting router

• Additional flags associated to advertised prefix(es). Notably, whether stateful

configuration, DHCP, is required

• MTU. Maximum datagram admeasurement that can be beatific by the host that all nodes in the same

subnet will accept

With the above-mentioned information, and if stateful agreement is not required, the end hosts

can body their own IPv6 addresses (with the interface ID either acquired from its MAC

address or about generated) and their absence acquisition table.

Figure 7-7 shows how router 2001:db8::4 advertises its attendance by a alternate multicast

(Ethernet multicast of 3333.0000.0001). This RA packet contains the router articulation local

Analyzing Risk for ND and Stateless Agreement 129

address FE80::200:BEFF:FEEF:0. This allotment of advice helps bounded hosts configure

themselves.

Figure 7-7 Router Advertisement Configuration

This stateless autoconfiguration will apparently be heavily acclimated in baby networks, such as at

home or in a baby enterprise. Larger networks will apparently await on DHCP to bigger track

IPv6 addresses and to accommodate added parameters, such as DNS servers and so on.