PIM-SM Version 2

PIM-SM Version 2

PIM-SM version 2 is specified in RFC 2362, June 1998. In this section, we will examine the differences between PIM-SM versions 1 and 2. The first major change is that version 2 messages are no longer encapsulated in IGMP messages but are encapsulated in IP packets with protocol number 103 (see Figure 7-18). PIM-SM version 2 messages are sent to the multicast group 224.0.0.13, ALL-PIM-ROUTERS.

Figure 7-18: Encapsulation of a PIM-SM version 2 packet in an IP datagram

The PIM-SM version 2 packet header has been modified from the version 1 packet header (see Figure 7-19). The types of messages identified in the packet header, along with the version 1 types, are listed in Table 7-3. As you can see, there have been a few modifications from Table 7-1.

Figure 7-19: PIM-SM version 2 packet header format

Table 7-3: PIM versions 1 and 2 message types

Type

Description Version 2

Description Version 1

0

Hello

Router query

1

Register (Sparse mode)

Same

2

Register-Stop (Sparse mode)

Same

3

Join/Prune

Same

4

Bootstrap (Sparse mode)

RP Reachability (Sparse mode)

5

Assert

Same

6

Graft (Dense mode)

Same

7

Graft-Ack (Dense mode)

Same

8

Candidate RP advertisement

Type not used

The router query message that was used as the Neighbor Discovery mechanism in version 1 has been replaced by the Hello message, shown in Figure 7-20.

Figure 7-20: PIM-SM Version 2 Hello message format

The Option fields for the Hello message are listed in Table 7-4 and the values of the holdtime in Table 7-5.

Table 7-4: Hello message Option fields

Option Type

Option Length

Option Value

1

2

Hold time

2—16

Reserved

Reserved

Table 7-5: Hello message holdtime values

Value

Description

0xFFFF

No time out

0

Immediate time out

Any other value

Neighbor time out value

A timeout value of 0xFFFF means that the neighbor never expires. This value has the affect of preventing periodic Hello messages being sent and is useful on a tariff connection, such as ISDN. Periodic Hellos would keep the link active, even in the absence of user data traffic, but you may not be happy receiving an ISDN bill for nothing more than periodic Hello traffic. A holdtime of zero signifies that the neighbor should immediately time out.

The Prune/Join message format has been modified, as shown in Figure 7-21. The encoded unicast and multicast address formats are shown in Figures 7-22 and 7-23.

Figure 7-21: PIM version 2 Join/Prune packet format

Figure 7-22: PIM version 2 encoded unicast address format

Figure 7-23: Encoded Group address format

Encoding value is 0 and represents the native encoding for the address family (see Table 7-6). Further encoded address examples are shown in Figures 7-23 and 7-24. Figure 7-25 displays the PIM-SM version 2 Assert message format.

Table 7-6: Address Family Assignments

Number

Description

0

Reserved

1

IP Version 4

2

IP Version 6

3

NSAP

4

HDLC (*-bit multidrop)

5

BBN 1822

6

802

7

E.163

8

E.164 (SMDS, Frame Relay, ATM)

9

F.69 (Telex)

10

X.121 (X.25, Frame Relay)

11

IPX

12

AppleTalk

13

DECnet IV

14

Banyan Vines

15	E.164 with NSAP format subaddress