Hash Table Guidelines For Creating Vlans - Avaya 580 User Manual

Hash Table and
Bucket memory
usage guidelines

Hash Table guidelines for creating VLANs

Maximum Number
of VLANs
Document No. 10-300077, Issue 2
The Avaya Multiservice switch provides 60K of memory that is used to
store hash tables and AFT buckets. In general, no more then 20K should be
used for Hash Tables, leaving 40K available for AFT entries (MAC
addresses). It is important to take into consideration the number of VLANs
that the switch will have when determining the hash table size for each
VLAN, as the total amount of memory used for the Hash Tables should not
exceed 20K. As more VLANs are created, the smaller each VLANs Hash
Table should be.
It is not advised to allow the total hash table memory usage to exceed 20K.
More than 20K will limit the potential for growth (i.e., address learning). If
your Avaya Multiservice switch is approaching this threshold, adjust the
Initial Hash Table Size accordingly.
For example, if you anticipate creating more than 20-30 VLANs, the Initial
Hash Table Size default setting must be reduced. The rule of thumb is the
following formula:
Number of VLANs times Initial Hash Table Size <20K
Example 1: 30 x 512 ~ 15K
Example 2: 1000 x 16 ~ 16K
* Note: When you create a VLAN, there are 18 internal MAC entries
automatically created for that VLAN. If you were to configure
Example 2, the switch would indicate that 36K of memory is
currently in use. This is because you have 16K of memory for
the VLAN Hash Tables and another 20K of memory used for
the 18,000 MAC entries.
In order to support the maximum number of VLANs, VLAN ID numbers
should be chosen from the range of 1 to 1000. The numbering of VLANs
has no impact on memory usage within the switch. The numbering of
VLANs only effects the total number of supported VLANs. This is not a
memory usage issue, however, it does effect the way the switch uses or
Hashes VLAN ID's. If VLAN ID's are used outside of the range of 1 to
1000, there is a possibility of unavailable VLAN ID's. This again does not
effect switch memory usage. If VLANs are already created with VLAN
ID's outside of the 1-1000 range, there is no need to reassign new VLAN
ID's. The only potential issue could be particular VLAN ID's might not be
available.
Managing the Address Forwarding Table
9-3