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Multicast Entry not Added. Hardware Table Full

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TitleMulticast Entry not Added. Hardware Table Full
Objective
Alleviate/Optimize the amount of entries for the ipmc (Layer 3 multicast) table to prevent the below log messages.

<Warn:Kern.IPv4Mc.Warning> Slot-<slot number>: IPv4 multicast entry not added.  Hardware L3 Table full. (Logged at most once per hour.)
Environment
A hash bucket in the L3 table has been exceeded and at least one IPv4 multicast host forwarding entry could not be added to the hardware. The L3 table is shared by IPv4 multicast and IPv4 and IPv6 unicast host entries. Any IPv4 multicast packet without an associated hardware forwarding entry will be slow path forwarded. This message will be logged at most 1 time per hour when new IPv4 unicast host forwarding entries trigger this condition.
  • EXOS
Procedure
  1. use the command "show iproute reserved-entries statistics" to see if entries are reaching HW limitation.  The "!" after the number shows that the HW limitation has been reached.
# show iproute reserved-entries statistics
                       |-----In HW Route Table----|   |--In HW L3 Hash Table--|
                       # Used Routes   # IPv4 Hosts   IPv4   IPv4   IPv6  IPv4
Slot  Type              IPv4   IPv6    Local Remote   Local  Rem.   Loc.  MCast
----  ---------------- ------ ------  ------ ------   -----  -----  ----  -----
1     X250e-48p           464!     0      17     31     177   1499     0      6
2     X250e-48t           464!     0      22     26     164   1596     0     13
3                           -      -       -      -       -      -     -      -
4                           -      -       -      -       -      -     -      -
5                           -      -       -      -       -      -     -      -
6                           -      -       -      -       -      -     -      -
7                           -      -       -      -       -      -     -      -
8                           -      -       -      -       -      -     -      -
 
Theoretical maximum for each resource type:
X440                       32     16      64     64     509    512   256 *  256
"e"-series                480    240     512    512    2045   2048  1024 * 2048
"a"-series              12256   6128    8189  12288    8189   8192  4096 * 5000

2. Use one or a combination of the below options to help optimize your multicast tables.
 
  1. This command conserves usage of the hardware Layer 3 multicast forwarding table.  Note this can only be done when this switch is not a PIM router or ipmcforwarding is enabled:
configure igmp snooping filters per-vlan
(to set it back to default set it to per-port)
 
  1. This command reduces what is stored for multicast entries in the format of (* AnySourceIP, GroupIP, VlanId), which is also referred to as (*, G):
configure igmp snooping forwarding-mode group-vlan
Or in newer EXOS versions

configure forwarding ipmc lookup-key group-vlan

(to set it back to default configure it to source-group-vlan)
  1. Disabling IGMP snooping on VLAN's where IGMP snooping is not required.  This removes all Multicast table entries from the VLAN, and will cause the multicast streams to be flooded in hardware.:
disable igmp snooping vlan <vlan_name>
 
  1. If the routing table is full you can use route compression.  Using longer network masks might not be necessary if they are a subset of other routes with shorter network masks using the same gateway(s). When IP route compression is enabled, these unnecessary routes are not provided to the Forwarding information Base (FIB) reducing the entries in the table.
enable iproute compression
Additional notes
Beginning in EXOS 15.4, the command in 2.b configure igmp snooping forwarding-mode group-vlan was replaced with configure forwarding ipmc lookup-key group-vlan.

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