Scale
The only limiting factor on FIB scale is the amount of memory allocated to each heap the FIB uses, and there are 2:
The main heap
The stats heap
Main Heap
The main heap is used to allocate all memory needed for the FIB data-structures. Each table, created by the user, i.e. with;
$ ip table add 1
or the default table, comprises 2 ip4_fib_t objects. The 'non-forwarding' ip4_fib_t contains all the entries in the table and, the 'forwarding' contains the entries that are matched against in the data-plane. The difference between the two sets are the entries that should not be matched in the data-plane. Each ip4_fib_t comprises an mtrie (for fast lookup in the data-plane) and a hash table per-prefix length (for lookup in the control plane).
To see the amount of memory consumed by the IPv4 tables use:
vpp# sh ip fib mem
ipv4-VRF:0 mtrie:335744 hash:4663
ipv4-VRF:1 mtrie:333056 hash:3499
totals: mtrie:668800 hash:8162 all:676962
this output shows two 'empty' (i.e. no added routes) tables. Each mtrie uses about 150k of memory, so each table about 300k.
Below the output having added 1M, 2M and 4M routes respectively:
vpp# sh ip fib mem
ipv4-VRF:0 mtrie:335744 hash:4695
totals: mtrie:335744 hash:4695 all:340439
vpp# sh ip fib mem
ipv4-VRF:0 mtrie:5414720 hash:41177579
totals: mtrie:5414720 hash:41177579 all:46592299
vpp# sh ip fib mem
ipv4-VRF:0 mtrie:22452608 hash:168544508
totals: mtrie:22452608 hash:168544508 all:190997116
IPv6 also has the concept of forwarding and non-forwarding entries, however for IPv6 all the forwarding entries are stored in a single hash table (same goes for the non-forwarding). The key to the hash table includes the IPv6 table-id.
To see the amount of memory consumed by the IPv4 tables use:
vpp# sh ip6 fib mem
IPv6 Non-Forwarding Hash Table:
Hash table ip6 FIB non-fwding table
7 active elements 7 active buckets
1 free lists
0 linear search buckets
arena: base 7f2fe28bf000, next 803c0
used 525248 b (0 Mbytes) of 33554432 b (32 Mbytes)
IPv6 Forwarding Hash Table:
Hash table ip6 FIB fwding table
7 active elements 7 active buckets
1 free lists
0 linear search buckets
arena: base 7f2fe48bf000, next 803c0
used 525248 b (0 Mbytes) of 33554432 b (32 Mbytes)
as we scale to 128k IPv6 entries:
vpp# sh ip6 fib mem
IPv6 Non-Forwarding Hash Table:
Hash table ip6 FIB non-fwding table
131079 active elements 32773 active buckets
2 free lists
[len 1] 2 free elts
0 linear search buckets
arena: base 7fed7a514000, next 4805c0
used 4720064 b (4 Mbytes) of 1073741824 b (1024 Mbytes)
IPv6 Forwarding Hash Table:
Hash table ip6 FIB fwding table
131079 active elements 32773 active buckets
2 free lists
[len 1] 2 free elts
0 linear search buckets
arena: base 7fedba514000, next 4805c0
used 4720064 b (4 Mbytes) of 1073741824 b (1024 Mbytes)
and 256k:
vpp# sh ip6 fib mem
IPv6 Non-Forwarding Hash Table:
Hash table ip6 FIB non-fwding table
262151 active elements 65536 active buckets
2 free lists
[len 1] 6 free elts
0 linear search buckets
arena: base 7fed7a514000, next 880840
used 8915008 b (8 Mbytes) of 1073741824 b (1024 Mbytes)
IPv6 Forwarding Hash Table:
Hash table ip6 FIB fwding table
262151 active elements 65536 active buckets
2 free lists
[len 1] 6 free elts
0 linear search buckets
arena: base 7fedba514000, next 880840
used 8915008 b (8 Mbytes) of 1073741824 b (1024 Mbytes)
and 1M:
vpp# sh ip6 fib mem
IPv6 Non-Forwarding Hash Table:
Hash table ip6 FIB non-fwding table
1048583 active elements 65536 active buckets
4 free lists
[len 1] 65533 free elts
[len 2] 65531 free elts
[len 4] 9 free elts
0 linear search buckets
arena: base 7fed7a514000, next 3882740
used 59254592 b (56 Mbytes) of 1073741824 b (1024 Mbytes)
IPv6 Forwarding Hash Table:
Hash table ip6 FIB fwding table
1048583 active elements 65536 active buckets
4 free lists
[len 1] 65533 free elts
[len 2] 65531 free elts
[len 4] 9 free elts
0 linear search buckets
arena: base 7fedba514000, next 3882740
used 59254592 b (56 Mbytes) of 1073741824 b (1024 Mbytes)
as can be seen from the output the IPv6 hash-table in this case was scaled to 1GB and 1million prefixes has used 56MB of it.
The main heap is also used to allocate objects that represent the FIB entries in the control and data plane (see The Control Plane and The Data Plane) such as fib_entry_t and load_balance_t. These come from the main heap because they are not protocol specific (i.e. they are used to represent either IPv4, IPv6 or MPLS entries).
With 1M prefixes allocated the memory usage is:
vpp# sh fib mem
FIB memory
Tables:
SAFI Number Bytes
IPv4 unicast 1 33619968
IPv6 unicast 2 118502784
MPLS 0 0
IPv4 multicast 1 1175
IPv6 multicast 1 525312
Nodes:
Name Size in-use /allocated totals
Entry 72 1048589/ 1048589 75498408/75498408
Entry Source 40 1048589/ 1048589 41943560/41943560
Entry Path-Extensions 76 0 / 0 0/0
multicast-Entry 192 6 / 6 1152/1152
Path-list 40 18 / 18 720/720
uRPF-list 16 14 / 14 224/224
Path 72 22 / 22 1584/1584
Node-list elements 20 1048602/ 1048602 20972040/20972040
Node-list heads 8 24 / 24 192/192
and with 2M
vpp# sh fib mem
FIB memory
Tables:
SAFI Number Bytes
IPv4 unicast 1 33619968
IPv6 unicast 2 252743040
MPLS 0 0
IPv4 multicast 1 1175
IPv6 multicast 1 525312
Nodes:
Name Size in-use /allocated totals
Entry 72 2097165/ 2097165 150995880/150995880
Entry Source 40 2097165/ 2097165 83886600/83886600
Entry Path-Extensions 76 0 / 0 0/0
multicast-Entry 192 6 / 6 1152/1152
Path-list 40 18 / 19 720/760
uRPF-list 16 18 / 18 288/288
Path 72 22 / 23 1584/1656
Node-list elements 20 2097178/ 2097178 41943560/41943560
Node-list heads 8 24 / 24 192/192
However, the situation is not a simple as that. All of the 1M prefixes added above were reachable via the same next-hop, so the path-list (and path) they use is shared. As prefixes are added that use different (sets of) next-hops, the number of path-lists and paths requires will increase.
Stats Heap
VPP collects statistics for each route. For each route VPP collects byte and packet counters for packets sent to the prefix (i.e. the route was matched in the data-plane) and packets sent via the prefix (i.e. the matching prefix is reachable through it - like a BGP peer). This requires 4 counters per route in the stats segment.
Below shows the size of the stats segment with 1M, 2M and 4M routes.
total: 1023.99M, used: 127.89M, free: 896.10M, trimmable: 830.94M
total: 1023.99M, used: 234.14M, free: 789.85M, trimmable: 668.15M
total: 1023.99M, used: 456.83M, free: 567.17M, trimmable: 388.91M