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Chapter 6 - Protocol Independent Multicast - Dense Mode

Cisco Multicast Routing & Switching
William R. Parkhurst
  Copyright © 1999 The McGraw-Hill Companies

PIM-DM Version 2
PIM-DM version 2 is specified in the IETF document draft-ietf-im-v2-dm-01.txt dated November 3, 1998. In this section we will examine the differences between PIM-DM 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 (Figure 6-24). PIM-DM version 2 messages are sent to the multicast group 224.0.0.13, ALL-PIM-ROUTERS.
Figure 6-24: Encapsulation of a PIM-DM version 2 packet in an IP datagram
Figure 6-26: PIM-DM Version 2 Hello message format
The PIM-DM version 2 packet header, shown in Figure 6-25, has been modified from the version 1 packet header (see Figure 6-6). The types of messages identified in the packet header along with the version 1 types are listed in Table 6-3. As you can see, there have been a few modifications from Table 6-1.
Figure 6-25: PIM-DM version 2 packet header format
Table 6-3: 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The router query message that was used as the neighbor discovery mechanism in version 1 has been replaced by the Hello message (see Figure 6-26).
The option fields for the Hello message are listed in Table 6-4 and the values of the hold time in Table 6-5.
Table 6-4: Hello Message Option Fields
Option Type
Option Length
Option Value
1
2
Hold time
2—16
Reserved
Reserved
Table 6-5: Hello Message Hold Time 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 times out. This value has the affect of preventing periodic hello messages from being sent. This is especially useful on a tariff connection such as an ISDN. Periodic hellos keep the link active even in the absence of user data traffic. 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 6-27 (compare to the version 1 format in Figure 6-14). The encoded unicast and multicast address formats are shown in Figures 6-28 through 6-31.
Figure 6-27: PIM version 2 Join/Prune Packet format
Figure 6-28: PIM version 2 encoded unicast address format
Figure 6-29: Encoded group address format
Figure 6-30: Encoded source address
Figure 6-31: PIM-DM version 2 Assert message format
Encoding value is 0 and represents the native encoding for the address family (see Table 6-6).
Table 6-6: 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
The Graft and Graft Acknowledgment message formats have not changed from version 1.

 


 
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