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HP 5500 Ei 5500 Si Switch Series Configuration Guide

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    							 335 
   Require-router-alert: disabled 
# Display MLD group information on Switch A. 
[SwitchA] display mld group 
Total 1 MLD Group(s). 
Interface group report information 
 Vlan-interface100(2001::1): 
  Total 1 MLD Groups reported 
   Group Address   Last Reporter   Uptime      Expires 
   ff3e::101       2001::2         00:02:04    00:01:15 
The output shows that the MLD reports sent from the hosts are forwarded to Switch A through the 
proxy interface, VLAN-interface 100 of Switch B. 
Troubleshooting MLD 
No member information on the receiver-side router 
Symptom 
When a host sends a message to announce its joining IPv6 multicast group G, no member information 
of multicast group G exists on the immediate router. 
Analysis 
•   The correctness of networking and interface conn ections and whether the protocol layer of the 
interface is up directly affect the generation of IPv6 group member information. 
•   IPv6 multicast routing must be enabled on the ro uter and MLD must be enabled on the interface 
connecting to the host.  
•   If the MLD version on the router interface is lower than that on the host, the router will not be able 
to recognize the MLD report from the host. 
•   If the  mld group-policy command has been configured on an in terface, the interface cannot receive 
report messages that fail to pass filtering. 
Solution 
1.  Check that the networking, interface connections,  and IP address configuration are correct. Check 
the interface information with the  display mld interface command. If no information is output, the 
interface is in an abnormal state. This is usually because you have configured the  shutdown 
command on the interface, the interface is  not properly connected, or the IPv6 address 
configuration is not correctly done. 
2.  Use the  display current-configuration  command to verify that the IPv6 multicast routing is enabled. 
If not, carry out the multicast ipv6 routing-enable command in system view to enable IPv6 multicast 
routing. In addition, enable MLD on the corresponding interface. 
3.  You can use the  display mld interface  command to verify that the MLD version on the interface is 
lower than that on the host.  
4.  Use the  display current-configuration interface  command to verify that no ACL rule has been 
configured to restrict the host from joining IPv6 mu lticast group G. If an IPv6 ACL is configured to 
restrict the host from joining IPv6 multicast gr oup G, the ACL must be modified to allow IPv6 
multicast group G to receive report messages.
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    							 336 
Inconsistent memberships on routers on the same subnet 
Symptom 
Different memberships are maintained on different MLD routers on the same subnet. 
Analysis 
•  A router running MLD maintains multiple paramet ers for each interface, and these parameters 
influence one another, forming very complicated relationships. Inconsistent MLD interface 
parameter configurations for routers on the same  subnet will surely result in inconsistent MLD 
memberships. 
•   Two MLD versions are available. Although router s running different MLD versions are compatible 
wi t h  h o s t s ,  a l l  ro u t e r s  o n  t h e  s a m e  s u b n e t  m u s t  r u n  t h e  s a m e  M L D  ve r s i o n.  I n c o n s i s t e n t  M L D  ve r s i o n s  
running on routers on the same subnet will  also lead to inconsistent MLD memberships. 
Solution 
1. Use the  display current-configuration  command to verify the MLD configuration information on the 
interface. 
2.  Use the  display mld interface  command on all routers on the same subnet to check the MLD timers 
for inconsistent configuration. 
3.  Use the  display mld interface  command to verify that the routers are running the same MLD 
version.
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    							 337 
Configuring IPv6 PIM (available only on the HP 
5500 EI) 
Overview 
Protocol Independent Multicast for IPv6 (IPv6 PIM) provi d e s  I P v 6  m u l t i c a s t  f o r w a r d i n g  by  l e ve r a g i n g  I P v 6  
unicast static routes or IPv6 unicast routing tables  generated by any IPv6 unicast routing protocol, such 
as RIPng, OSPFv3, IS-ISv6, or BGP4+. IPv6 PIM uses an IPv6 unicast routing table to perform reverse 
path forwarding (RPF) check to implement IPv6 mult icast forwarding. Independent of the IPv6 unicast 
routing protocols running on the device, IPv6 mult icast routing can be implemented as long as the 
corresponding IPv6 multicast routing entries are created through IPv6 unicast routes. IPv6 PIM uses the 
reverse path forwarding (RPF) mechanism to implement IPv6 multicast forwarding. When an IPv6 
multicast packet arrives on an interface of the device, RPF check is performed on it. If the RPF check 
succeeds, the device creates the corresponding routin g entry and forwards the packet. If the RPF check 
fails, the device discards the packet. For more information about RPF, see  Configuring IPv6 multicast 
r

outing and forwarding  (available only on the HP 5500 EI) .  
Based on the implementation mechanism, IPv6 PIM supports the following types:  
•   Protocol Independent Multicast–Dense Mode for IPv6 (IPv6 PIM-DM) 
•   Protocol Independent Multicast–Sparse Mode for IPv6 (IPv6 PIM-SM) 
•   Bidirectional Protocol Independent Multicast for IPv6 (IPv6 BIDIR-PIM) 
•   Protocol Independent Multicast Source-Specific Multicast for IPv6 (IPv6 PIM-SSM) 
To  f a ci l i t a t e  d e s c r i p t i o n,  a  n e t w o r k  c o m p ri s i n g  I P v 6  P I M – s u p p o r t i n g  ro u t e r s  i s  re f e r re d  t o  a s  a n   I P v 6  P I M  
domain in this document. 
The term router in this document refers to both routers and Layer 3 switches. 
The term interface in the IPv6 PIM features refers to Layer 3 interfaces, including VLAN interfaces and 
route-mode (or Layer 3) Ethernet ports. You can set an  Ethernet port to operate in route mode by using the 
port  link-mode  route  command (see  Layer 2—LAN Switching Configuration Guide ). 
IPv6 PIM-DM overview 
IPv6 PIM-DM is a type of dense mode IPv6 multicast  protocol. It uses the push mode for IPv6 multicast 
forwarding, and is suitable for small-sized networks  with densely distributed IPv6 multicast members. 
The basic implementation of IPv6 PIM-DM is as follows:  
•   IPv6 PIM-DM assumes that at least one IPv6 multicast group member exists on each subnet of a 
network. Therefore, IPv6 multicast data is flooded to all nodes on the network. Then, branches 
without IPv6 multicast forwarding are pruned from the forwarding tree, leaving only those branches 
that contain receivers. This flood-and-prune process takes place periodically. That is, pruned 
branches resume IPv6 multicast forwarding when  the pruned state times out and then data is 
flooded again down these branches, and then the branches are pruned again.  
•   When a new receiver on a previously pruned branch joins an IPv6 multicast group, to reduce the 
join latency, IPv6 PIM-DM uses the graft mechan ism to resume IPv6 multicast data forwarding to 
that branch.
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    							 338 
In general, the IPv6 multicast forwarding path is a source tree. That is, it is a forwarding tree with the IPv6 
multicast source as its root and IPv6 multicast group members as its leaves. Because the source tree 
is the shortest path from the IPv6 multicast source to the receivers, it is also called shortest path tree 
(SPT).  
The working mechanism of IPv6 PIM-DM is summarized as follows:  
•  Neighbor discovery 
•   SPT establishment 
•   Graft 
•   Assert 
Neighbor discovery 
In an IPv6 PIM domain, a PIM router discovers IPv6 PIM neighbors, maintains IPv6 PIM neighboring 
relationships with other routers, and builds and main tains SPTs by periodically multicasting IPv6 PIM 
hello messages to all other IPv6 PIM routers on the local subnet.  
 
  NOTE: 
Every IPv6 PIM enabled interface on a router sends he llo messages periodically and, therefore, learns the
IPv6 PIM neighboring information pertinent to the interface. 
 
SPT establishment 
The process of constructing an SPT is the flood and prune process.  
1.  In an IPv6 PIM-DM domain, an IPv6 multicast sour ce first floods IPv6 multicast packets when it 
sends IPv6 multicast data to IPv6 multicast group G. The packet undergoes an RPF check. If the 
packet passes the RPF check, the router creates an (S, G) entry and forwards the packet to all 
downstream nodes in the network. In the flooding  process, an (S, G) entry is created on all the 
routers in the IPv6 PIM-DM domain.  
2.  The nodes without downstream rece ivers are pruned. A router that has no downstream receivers 
sends a prune message to the upstream node to  notify the upstream node to delete the 
corresponding interface from the outgoing interface list in the (S, G) entry and stop forwarding 
subsequent packets addressed to that IPv6  multicast group down to this node.  
An (S, G) entry contains the multicast source addr ess S, IPv6 multicast group address G, outgoing 
interface list, and incoming interface. 
For a given IPv6 multicast stream, the interface that  receives the IPv6 multicast stream is referred to 
as upstream, and the interfaces  that forward the IPv6 multicast stream are referred to as 
downstream. 
A leaf router first initiates a prune process. As shown in  Figure 90, a r
 outer without any receiver attached 
to it (the router connected with Host A, for exam ple) sends a prune message, and this prune process 
continues until only necessary branches remain in the IPv6 PIM-DM domain. These branches constitute 
the SPT.
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    							 339 
Figure 90 SPT establishment in an IPv6 PIM-DM domain 
 
 
The flood-and-prune process takes place periodically. A pruned state timeout mechanism is provided. A 
pruned branch restarts multicast forwarding when th e pruned state times out and then is pruned again 
when it no longer has any multicast receiver.  
 
  NOTE: 
Pruning has a similar implementation in IPv6 PIM-SM. 
 
Graft 
When a host attached to a pruned node joins an IPv6  multicast group, to reduce the join latency, IPv6 
PIM-DM uses the graft mechanism to resume IPv6 mu lticast data forwarding to that branch. The process 
is as follows:  
1.  The node that needs to receive IPv6 multicast dat a sends a graft message toward its upstream node 
as a request to join the SPT again.  
2.  After receiving this graft message, the upstream  node puts the interface on which the graft was 
received into the forwarding state and responds  with a graft-ack message to the graft sender.  
3. If the node that sent a graft message does not re ceive a graft-ack message from its upstream node, 
it keeps sending graft messages at a configurable  interval until it receives an acknowledgment 
from its upstream node.  
Assert 
Where more than one multicast routers exists, the as sert mechanism shuts off duplicate IPv6 multicast 
flows onto the same multi-access netw ork. It does this by electing a unique IPv6 multicast forwarder on 
the multi-access network. 
Source
Server Host A
Host B
Host C ReceiverReceiver
IPv6 multicast packets
SPT
Prune message
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    							 340 
Figure 91 Assert mechanism 
 
 
As shown in Figure 91, af ter Router A and Router B receive an (S, G) IPv6 multicast packet from the 
upstream node, they both forward the packet to the lo cal subnet. As a result, the downstream node Router 
C receives two identical multicast packets, and both Ro uter A and Router B, on their own local interface, 
receive a duplicate IPv6 multicast packet that the ot her has forwarded. After detecting this condition, 
both routers send an assert message to all IPv6 PIM  routers on the local subnet through the interface that 
received the packet. The assert message contains the multicast source address (S), the multicast group 
address (G), and the preference and metric of the IPv6 unicast route/IPv6 MBGP route/IPv6 multicast 
static route to the source. By comparing these param eters, either Router A or Router B becomes the 
unique forwarder of the subsequent (S, G) IPv6 multicast packets on the multi-access subnet. The 
comparison process is as follows:  
1.  The router with a higher preference to the source wins.  
2. If both routers have the same preference to the sour ce, the router with a smaller metric to the source 
wins.  
3.  If a tie exists in the route metric to the source, th e router with a higher IPv6 link-local address wins.  
IPv6 PIM-SM overview 
IPv6 PIM-DM uses the flood-and-prune principle to  build SPTs for IPv6 multicast data distribution. 
Although an SPT has the shortest path, it is built with a low efficiency. Therefore the PIM-DM mode is not 
suitable for large-sized and medium-sized networks.  
IPv6 PIM-SM is a type of sparse-mode IPv6 multicast protocol. It uses the pull mode for IPv6 multicast 
forwarding, and is suitable for large-sized and me dium-sized networks with sparsely and widely 
distributed IPv6 multicast group members.  
The basic implementation of IPv6 PIM-SM is as follows:  
•   IPv6 PIM-SM assumes that no hosts need to receive IPv6 multicast data. In the IPv6 PIM-SM mode, 
routers must specifically request a particular IPv6 multicast stream before the data is forwarded to 
them. The core task for IPv6 PIM-SM to implement IPv6 multicast forwarding will build and maintain 
rendezvous point trees (RPTs). An RPT is rooted at a router in the IPv6 PIM domain as the common 
node, or rendezvous point (RP), through which the IPv6 multicast data travels along the RPT and 
reaches the receivers.  
•   When a receiver is interested in the IPv6 multicas t data addressed to a specific IPv6 multicast group, 
the router connected to this receiver sends a join  message to the RP corresponding to that IPv6 
multicast group. The path along which the message goes hop by hop to the RP forms a branch of 
the RPT.
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    							 341 
•  When an IPv6 multicast source sends IPv6 multicast streams to an IPv6 multicast group, the 
source-side designated router (DR) first registers the multicast source with the RP by sending register 
messages to the RP by unicast until it receives a register-stop message from the RP. The arrival of a 
register message at the RP triggers the establishment of an SPT. The IPv6 multicast source sends 
subsequent IPv6 multicast packets along the SPT to the RP. After reaching the RP, the IPv6 multicast 
packet is duplicated and delivered to the receivers along the RPT.  
 
  NOTE: 
IPv6 multicast traffic is duplicated only where the di stribution tree branches, and this process automaticall
y
repeats until the IPv6 multicast traffic reaches the receivers.   
The working mechanism of IPv6 PIM-SM is summarized as follows:  
•  Neighbor discovery 
•   DR election 
•   RP discovery 
•   Embedded RP 
•   RPT establishment  
•   IPv6 Multicast source registration 
•   Switchover to SPT 
•   Assert 
Neighbor discovery 
I P v 6  P I M - S M  u s e s  t h e  s i m i l a r  n e i g h b o r  d i s c o v e r y  m e c h a n i s m  a s  I P v 6  P I M - D M  d o e s .  Fo r  m o r e  i n f o r m a t i o n ,  
see  Neighbor discovery .  
DR election 
IPv6 PIM-SM also uses hello messages to elect a  DR for a multi-access network (such as a LAN). The 
elected DR will be the only IPv6 multicast  forwarder on this multi-access network.  
In the case of a multi-access network, a DR must be elected, no matter this network connects to IPv6 
multicast sources or to receivers. The DR at the receiver side sends join messages to the RP; the DR at the  
IPv6 multicast source side sends register messages to the RP.  
A DR is elected on a multi-access subnet by means of  comparison of the priorities and IPv6 link-local 
addresses carried in hello messages.  
MLD must be enabled on a device that acts as a receiver-side DR before receivers attached to this device 
can join IPv6 multicast groups through this DR. 
For more information about MLD, see  Configuring MLD (available only on the HP 5500 EI) .
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    							 342 
Figure 92 DR election 
 
 
As shown in Figure 92, the D R election process is as follows:  
1. Routers on the multi-access network send hello messages to one another. The hello messages 
contain the router priority for DR election. The router with the highest DR priority will become the 
DR. 
2. In the case of a tie in the router priority, or if any router in the network does not support carrying 
the DR-election priority in hello messages, the ro uter with the highest IPv6 link-local address will 
win the DR election.  
When the DR works abnormally, a timeout in receiving hello message triggers a new DR election process 
among the other routers.  
RP discovery 
The RP is the core of an IPv6 PIM-SM domain. For a small-sized, simple network, one RP is enough for 
forwarding IPv6 multicast information throughout the ne twork, and the position of the RP can be statically 
specified on each router in the IPv6 PIM-SM domain. In most cases, however, an IPv6 PIM-SM network 
covers a wide area and a huge amount of IPv6 mult icast traffic must be forwarded through the RP. To 
lessen the RP burden and optimize the topological structure of the RPT, you can configure multiple 
candidate-RPs (C-RPs) in an IPv6 PIM-SM domain. Am ong them, an RP is dynamically elected through the 
bootstrap mechanism. Each elected RP serves a diff erent multicast group range. For this purpose, you 
must configure a bootstrap router (BSR). The BSR serves as the administrative core of the IPv6 PIM-SM 
d o m a i n .  A n  I P v 6  P I M - S M  d o m a i n  c a n  h a v e  o n l y  o n e  B S R, but can have multiple candidate-BSRs (C-BSRs). 
If the BSR fails, a new BSR is automatically elected from the C-BSRs to avoid service interruption. 
 
  NOTE: 
•  An RP can serve IPv6 multiple multicast groups or all IPv6 multicast groups. Only one RP can serve a 
given IPv6 multicast group at a time. 
•   A device can serve as a C-RP and a C-BSR at the same time.  
 
As shown in Figure 93 , each C-RP periodically unicasts its ad vertisement messages (C-RP-Adv messages) 
to the BSR. A C-RP-Adv message contains the addres s of the advertising C-RP and the IPv6 multicast 
group range it serves. The BSR collects these advert isement messages and chooses the appropriate C-RP 
information for each multicast group to form an RP-set, which is a database of mappings between IPv6
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    							 343 
multicast groups and RPs. The BSR then encapsulates the RP-set in the bootstrap messages it periodically 
originates and floods the bootstrap messages  (BSMs) to the entire IPv6 PIM-SM domain. 
Figure 93  BSR and C-RPs 
 
 
Based on the information in the RP-sets, all routers in the network can calculate the location of the 
corresponding RPs based on the following rules:  
1. The C-RP with the highest priority wins.  
2. If all the C-RPs have the same priority, their  hash values are calculated through the hashing 
algorithm. The C-RP with the largest hash value wins.  
3.  If all the C-RPs have the same priority and hash va lue, the C-RP that has the highest IP address wins.   
The hashing algorithm used for RP calculation is Value (G, M, C
i) = (1 10 3 51524 5  *  (  (110 3 51524 5  *  ( G  
& M) + 12345) XOR C
i) + 12345) mod 231.  
Table 11  Values in the hashing algorithm 
Value Descri
ption 
Value   Hash value. 
G  The digest from the exclusive-or (XOR) op
eration between the 32-bit segments of 
the IPv6 multicast group address. For example, if the IPv6 multicast address is 
FF0E:C20:1A3:63::101, G = 0 xFF0E0C20 XOR 0x01A30063 XOR 
0x00000000 XOR 0x00000101. 
M  Hash mask length. 
Ci The digest from the exclusive-or (XOR) op
eration between the 32-bit segments of 
the C-RP IPv6 address. For example, if  the IPv6 address of the C-RP is 
3FFE:B00:C18:1::10, Ci = 0x3FFE0B00 XOR 0x0C180001 XOR 
0x00000000 XOR 0x00000010. 
&  Logical operator of and. 
XOR Logical operator of exclusive-or. 
mod Modulo operator, which gives the remainder of an integer division.
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    							 344 
Embedded RP 
The embedded RP mechanism enables a router to resolve the RP address from an IPv6 multicast address 
so that the IPv6 multicast group is mapped to an RP. This RP can take the place of the statically configured 
RP or the RP dynamically calculated based on the BSR mechanism. The DR does not need to identif y the 
RP address beforehand. The specific process is as follows.  
At the receiver side, the following occur:  
1.  A receiver host initiates an MLD report to announce  that it is joining an IPv6 multicast group.  
2. After receiving the MLD report, the receiver-side DR resolves the RP address embedded in the IPv6 
multicast address and sends a join message to the RP.  
At the IPv6 multicast source side, the following occur:  
1.  The IPv6 multicast source sends IPv6 multic ast traffic to the IPv6 multicast group.  
2. The source-side DR resolves the RP address embedd ed in the IPv6 multicast address, and sends a 
register message to the RP.  
RPT establishment 
Figure 94  RPT establishment in an IPv6 PIM-SM domain 
 
 
As shown in Figure 94, the pr ocess of building an RPT is as follows:  
1. When a receiver joins IPv6 multicast group G, it us es an MLD report message to inform the directly 
connected DR.  
2.  After getting the IPv6 multicast gr oup G’s receiver information, the DR sends a join message, which 
is forwarded hop by hop to the RP that  corresponds to the multicast group.  
3. The routers along the path from the DR to the RP fo rm an RPT branch. Each router on this branch 
generates a (*, G) entry in its forwarding table.  The asterisk means any IPv6 multicast source. The 
RP is the root of the RPT, and the DRs are the leaves of the RPT. 
The IPv6 multicast data addressed to the IPv6 mult icast group G flows through the RP, reaches the 
corresponding DR along the established RPT, and finally is delivered to the receiver.  
When a receiver is no longer interested in the IP v6 multicast data addressed to a multicast group G, the 
directly connected DR sends a prune message, which goes hop by hop along the RPT to the RP. After 
receiving the prune message, the upstream node deletes the interface connected with this downstream 
Source
Server Host A
Host B
Host C ReceiverReceiver
IPv6 multicast packets
RPT
Join message RP DR
DR
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