+++ /dev/null
-$Id: IMPLEMENTATION.txt,v 1.2 2005/02/15 17:10:03 gdt Exp $
-
-This file contains notes about the internals of the BGP
-implementation. The initial impetus is understanding the memory usage
-of Quagga'a BGP implementation. There may be some inaccuracies; it is
-in the repository in the hopes that it will be significantly more
-helpful than not.
-
-* FILES
-
-bgp_advertise.[hc]:
- data structures: advertised prefixes, attributes
-
-bgp_aspath.[hc]:
- struct aspath:
- These are stored in a hash, apparently in wire format.
-
-bgp_attr.[hc]:
- struct attr: contains all attributes
- size(ILP32) 26 words/104 bytes (poor packing, v6/multicast is 10)
-
- bgp_attr_parse: origin, aspath, next hop probably most of interest
- bgp_attr_origin: set flag bit
- bgp_attr_aspath: put in refcounted hash table, so share pointer
- bgp_attr_nexthop: store in attribute structure
-
-bgp_btoa.c: ? test program
-
-bgp_clist.[hc]:
- data structures: community lists (including permit/deny state)
-
-bgp_community.[hc]:
- data structures: community atttributes (multiple communities per struct)
-
-bgp_damp.[hc]:
- per-route damping data, and damping control information
-
-bgp_debug.[hc]:
- debugging support (vty config, dump of packets)
-
-bgp_dump.[hc]:
- MRT-compatible dump format routines
-
-bgp_ecommunity.[hc]:
- Extended communities attributes (multiple ecommmunities per struct)
-
-bgp_filter.[hc]:
- AS path access list filtering
-
-bgp_fsm.[hc]:
- Per-peer state machine for TCP connection, hold time, etc.
-
-bgp_main.c:
- Daemon startup.
-
-bgp_mplsvpn.[hc]:
- parsing of attribute structures for MPLS VPNs [need better description]
-
-bgp_network.[hc]:
- Opening and binding of sockets, finding addresses for interfaces
-
-bgp_nexthop.[hc]:
- data structures: Nexthop cache [not clear how used, if truly cache
- in sense of memoization, or something else]
-
- importing EGP routes into IGP (thread created)
- "scanning" (thread created)
- bgp_scan: has useful clues to data structure complexity. Scanning
- process iterates over database of received advertisements, and
- builds 'cache' structure.
-
-bgp_open.[ch]:
- Open messages, and capability negotiation
-
-bgp_packet.[hc]
- sending and receiving of UPDATE/WITHDRAW
- collision resolution for simultanteous opens
- bgp_read: top-level read routine: reads whole packet (nonblocking)
- and dispatches to per-message-type receive
-
- bgp_update_receive:
- calls bgp_attr_parse
- reads nrli into struct bgp_nrli update
-
- uninterning of aspath, community, ecommmunity, cluster,
- transit which were interned in bgp_attr_parse
-
-bgp_regex.[ch]:
- Glue to convert BGP regexps to standard (_ means many things).
-
-bgp_route.[hc]:
- data structures: routes as received, static routes
- Application of filters. Lots of route processing.
-
- bgp_nlri_parse:
- sanity checks, then calls bgp_update with peer, prefix, attributes pointer
-
- bgp_update: bgp_update_main, then RS processing
-
- bgp_update_main:
- find 'struct bgp_node *' for this afi/safi
- look for route in table, then 'intern' attributes
- ** interning is process of
- looking for data in hash table, and putting there if missing, refcnt
- using pointer to existing data
- many validity checks
- get new struct bgp_info (10 words/40 bytes)
- call bgp_info_add with rn and bgp_info
- call bgp_process
-
-bgp_routemap.c
- implementation of route maps (match and set)
-
-bgp_snmp.c
- SNMP glue. Not particularly interesting except to add variables or
- debug SNMP.
-
-bgp_table.[hc]
- data structures: struct bgp_table, struct bgp_node
- allocation/lookup/utility operations - not a lot of protocol processin
-
-bgp_vty.[hc]
- protocol-wide vty hooks
-
-bgp_zebra.[hc]
- Processing interface events from zebra, redistribution of routes.
-
-bgpd.h
- struct bgp_master: daemon main data structure
- struct bgp: per-instance structure
- struct peer_group
- struct bgp_notify: (in-core representation of wire format?)
- struct bgp_nexthop: (v4 and v6 addresses, *ifp)
- struct bgp_rd: router distinguisher: 8 octects
- struct bgp_filter: distribute, prefix, aslist, route_maps
- struct peer: neighbor structure (very rich/complex)
- struct bgp_nlri: reference to wire format
- #define of protocol constants
- attribute type codes
- fsm states/events
- timer values
-
-bgpd.c
- instance/peer allocation
- configuration
- initialization/termination
-
-* DATA STRUCTURE SIZES
-
-Question: How much memory does quagga's bgpd use as a function of
-state received from peers?
-
-It seems that a struct bgp_info is kept for each prefix. The "struct
-attr *" is interned, and variables within that are interned. So, 40
-bytes are kept per received prefix, plus interned shared values. This
-could be 36 if 'int suppress' where changed to a u_char and moved to
-be with the other u_chars. Without MPLS, this could be 32 bytes.
-Note that 8 bytes of this is linked list overhead, meaning that 24
-bytes are the raw per-prefix storage requirements.
-
-Also, a struct bgp_damp_info is apparently maintained per route; this
-is fairly large (about 44 bytes).
-
-[TODO: the role of struct bgp_node.]
-
-* TIME COMPLEXITY
-
-It appears that received prefixes from each peer are stored in a
-linked list.
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