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+.. _scale:
+
+Scale
+-----
+
+The only limiting factor on FIB scale is the amount of memory
+allocated to each heap the FIB uses, and there are 4:
+
+* The IP4 heap
+* The IP6 heap
+* The main heap
+* The stats heap
+
+
+IP4 Heap
+--------
+
+The IPv4 heap is used to allocate the memory needed for the
+data-structures within which the IPv4 prefixes are stored. Each
+table, created by the user, i.e. with;
+
+.. code-block:: console
+
+   $ 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:
+
+.. code-block:: console
+                
+ vpp# sh ip fib mem
+ ipv4-VRF:0 mtrie:333056 hash:3523
+ ipv4-VRF:1 mtrie:333056 hash:3523
+ totals: mtrie:666112 hash:7046 all:673158
+
+ Mtrie Mheap Usage: total: 32.06M, used: 662.44K, free: 31.42M, trimmable: 31.09M
+     free chunks 3 free fastbin blks 0
+     max total allocated 32.06M
+ no traced allocations
+
+this output shows two 'empty' (i.e. no added routes) tables. Each
+mtrie uses about 150k of memory, so each table about 300k. the total
+heap usage statistics for the IP4 heap are shown at the end.
+
+
+Below the output having added 1M, 2M and 4M routes respectively:
+
+.. code-block:: console
+
+ vpp# sh ip fib mem
+ ipv4-VRF:0 mtrie:335744 hash:4695
+ totals: mtrie:335744 hash:4695 all:340439
+
+ Mtrie Mheap Usage: total: 1.00G, used: 335.20K, free: 1023.74M, trimmable: 1023.72M
+     free chunks 3 free fastbin blks 0
+     max total allocated 1.00G
+ no traced allocations
+
+.. code-block:: console
+
+ vpp# sh ip fib mem
+ ipv4-VRF:0 mtrie:5414720 hash:41177579
+ totals: mtrie:5414720 hash:41177579 all:46592299
+
+ Mtrie Mheap Usage: total: 1.00G, used: 46.87M, free: 977.19M, trimmable: 955.93M
+     free chunks 61 free fastbin blks 0
+     max total allocated 1.00G
+ no traced allocations
+
+.. code-block:: console
+
+ vpp# sh ip fib mem
+ ipv4-VRF:0 mtrie:22452608 hash:168544508
+ totals: mtrie:22452608 hash:168544508 all:190997116
+
+ Mtrie Mheap Usage: total: 1.00G, used: 198.37M, free: 825.69M, trimmable: 748.24M
+     free chunks 219 free fastbin blks 0
+     max total allocated 1.00G
+ no traced allocations
+
+VPP was started with a 1G IP4 heap.
+
+IP6 Heap
+--------
+
+The IPv6 heap is used to allocate the memory needed for the
+data-structure within which the IPv6 prefixes are stored. IPv6 also
+has the concept of forwarding and non-forwarding entries, however for
+IPv6 all the forwardind 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:
+
+.. code-block:: console
+
+ 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:
+
+.. code-block:: console
+
+ 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:
+
+.. code-block:: console
+
+ 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:
+
+.. code-block:: console
+
+ 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 heap in this case was scaled
+to 1GB and 1million prefixes has used 56MB of it.
+
+
+Main Heap
+---------
+
+The main heap is used to allocate objects that represent the FIB
+entries in the control and data plane (see :ref:`controlplane` and
+:ref:`dataplane`) 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:
+
+.. code-block:: console
+
+ 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
+
+.. code-block:: console
+       
+ 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.
+
+.. code-block:: console
+
+ 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
+
+VPP was started with a 1G stats heap.
+