Agregacions BGP

Depenent de l'escenari de xarxa ens pot interessar anunciar 1 ruta que n'englobi 2,5,10... Per exemple, perquè volem anunciar dues xarxes /27 consecutives si sabem que formen un /26, d'aquesta forma ens estalviem 1 ruta. Aquest exemple pot ser una mica absurt, però a gran escala pot ser necessari. Només s'ha de vigilar, que es faci servir en una zona on la conectivitat sigui final, que si mai es "redunda" la zona ( les rutes sense agregar ens arribin per un altre canto, hi haurà pollastre de rutes, que encara no tinc clar com es resoldria.

CAS 1: Un Supernode anuncia 2 xarxes creades en el seu router. Fins ara anunciava 2 xarxes, 10.228.54.0/25 i 10.228.54.128/25 La configuracio en aquest cas seria la seguent:

# jan/27/2013 22:16:31 by RouterOS 5.21
# software id = YPVN-F2XA
#
/routing bgp aggregate
add advertise-filter="" attribute-filter="" disabled=no include-igp=yes inherit-attributes=yes instance=default prefix=10.228.54.0/24 summary-only=yes \
    suppress-filter=""

Cas 2: Un supernode anuncia 2 xarxes, que li venen anunciades per un altre peer. 10.228.54.0/25 i 10.228.54.128/25 Seria la mateixa configuració, però sense incloure la taula igp, ja que la ruta l'origen de la ruta és ebgp.

# jan/27/2013 22:16:31 by RouterOS 5.21
# software id = YPVN-F2XA
#
/routing bgp aggregate
add advertise-filter="" attribute-filter="" disabled=no include-igp=no inherit-attributes=yes instance=default prefix=10.228.54.0/24 summary-only=yes \
    suppress-filter=""

Parametres d'una aggregacio:

include-igp= quan l'agregació prove d'origen IGP s'ha d'activar.

inherit-attributes= quan s'activa la ruta agafa atributs originals, origen i AS PATH's....

summary-only= aquesta opcio ens borra automaticament les rutes agregades. Sino segurien anuncinat-se

Recomanació que fa Mikrotik sobre el nº de rutes a gestionar per router

Question: How much memory is required to keep the global BGP route table?
Our recommendations are at least 256 MB RAM for a single copy of the table and at least 512 MB RAM for two or three copies.

Assuming the Internet route table size ~300 000 routes, for the first copy of the table, with routes resolved and active, about 155 MB extra memory is needed. This is only for the first copy specifically, the amount of RAM needed for each additional copy of the table is significantly less than that number.

RAM usage on RB1000 (BGP feed size 301 480 routes, no redistribution):

No BGP routes: 26 MB
Single copy: 181 MB
Two copies: 241 MB
Three copies: 299 MB
Memory requirements will increase if incoming routing filters that change route attributes are used. That happens because unchanged copy of the route attributes received also will be stored in RAM, to be used in case of later routing filter change.

The requirements will also increase depending on count of peers to which routes are advertised.

It is not recommended to turn on SNMP on routers with full BGP feed!