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$Id: IMPLEMENTATION.txt,v 1.1 2005/02/10 16:38:09 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, and this has
its own struct attr. aspath, etc. are 'interned' and shared.
So, it seems that 144 bytes are used per received prefix, plus storage
for all unique aspaths received.
* TIME COMPLEXITY
It appears that received prefixes from each peer are stored in a
linked list.
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