3Com 4007, Руководство по внедрению, Страница: 486 / 684

486 C
HAPTER
19: O
PEN
S
HORTEST
P
ATH
F
IRST
(OSPF) R
OUTING
The estimate (maxRoutingTableSize) of the maximum number of routing
table entries the system can hold for a given memory size is a hardcoded
value. On extended memory systems this value is 51200. On systems
without extended memory this value is only 1024.
Applying the formula to extended memory systems yields a default OSPF
current partition maximum size of 4,200,000. (Due to memory overhead,
the actual number of routing table entries possible is somewhat different
than the 51200 maximum.)
Even though currently unallocated, this memory is not available to other
protocols.
Allocated Memory Size
The
allocated memory size
is the size of the memory that is currently
allocated to OSPF. The minimum size this allocated memory partition can
default to is 100000.
The system allocates more memory as required in 100000-byte chunks
until the current partition maximum size is reached.
Running Out of
Memory — Soft
Restarts
An attempt to allocate memory past the OSPF current partition maximum
size generates a soft restart condition that momentarily causes the router
to go down. This may occur, for example, because:
■
The routing table grew suddenly because it received a large number of
external link state advertisements (LSAs), such as RIP routes learned
from an ASBR, that had to be added to the internal database.
■
The router is an area border router (ABR) for multiple large subareas
and thus has a much larger than usual routing table.
The
ip ospf statistics
option displays the number of soft restarts.
After the soft restart, the system frees all of its OSPF memory, disables its
interfaces, reenables them, and reconstructs the router tables from
scratch. This process attempts to free and defragment enough unused
memory so that OSPF has sufficient memory to continue. If the soft
restart does not free enough memory, the soft restart condition
repeats — and the router continues to thrash for memory.
If the softRestarts statistic shows that the default memory allocation
scheme is too small for your router, then you must use one of the other
two memory allocation options described next.