Routing Questions: Difference between revisions

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=====Question: How does /ip route check-gateway work? =====
=====Question: How does /ip route check-gateway work? =====


check-gateway sends pings every 10 seconds. if two successive pings fail, the gateway is considered dead.
:check-gateway sends pings every 10 seconds. if two successive pings fail, the gateway is considered dead.
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=====Question: I have one /24 network advertised to two BGP peers using "/routing bgp networks" facility. How do I advertise a higher path cost to one of the peers?=====
 
You have to change the way you are redistributing your network, as filters are not applied to routes advertised from "/routing bgp networks". In most cases the network is connected directly to your router, so it's enough to set BGP instance to redistribute directly connected routes:
 
/routing bgp instance set default redistribute-connected=yes
 
: To filter out all other connected networks except the needed one, create a routing filter for the BGP instance,
 
/routing filter add invert-match=yes prefix=10.0.0.0/24 action=discard name=InstanceOutFilter
 
:then set filter "InstanceOutFilter" as the out-filter for "default" BGP instance.
 
/routing bgp instance set default out-filter=InstanceOutFilter
 
: To communicate a lower preference value (higher path cost) to one of the peers, you have to prepend your AS number multiple times to the BGP AS_PATH attribute
 
/routing filter add prefix=10.0.0.0/24 set-bgp-prepend=4 name=Peer1OutFilter
/routing bgp peer set Peer1 out-filter=Peer1OutFilter
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=====Question: I have a /22 (say 10.0.0.0/22) assigned IP space, split internally down into /30's, /28's, etc. Is it possible just to announce the /22 space via BGP with routing-test package?=====
 
Yes, it is possible.  Do the following:
 
:1.  add an empty bridge interface:
/interface bridge add name=loopback
:2.  assign a /22 address to the bridge interface:
/ip address add address=10.0.0.1/22 interface=loopback
:3.  create a routing filter that filters out all prefixes except the /22 one
/routing filter add invert-match=yes prefix=10.0.0.0/22 prefix-length=22 action=discard name=myfilter
:4.  set filter "myfilter" as the out-filter for "default" BGP instance
/routing bgp instance set default out-filter=myfilter
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=====Question: How to blackhole a network?=====
=====Question: How to blackhole a network?=====


There are two ways to blackhole a network. First, you can do this manually by adding a blackhole route to the routing table, for example, to blackhole a 10.0.0.0/8 network, issue the following command:
:There are two ways to blackhole a network. First, you can do this manually by adding a blackhole route to the routing table, for example, to blackhole a 10.0.0.0/8 network, issue the following command:
  /ip route add dst-address=10.0.0.0/8 kernel-type=blackhole
  /ip route add dst-address=10.0.0.0/8 type=blackhole
Routing filters are the other mean to blackhole a network. To create a routing filter that automatically blackholes all prefixes in 10.0.0.0/8 in the BGP feed, issue the following command:
:Routing filters are the other mean to blackhole a network. To create a routing filter that automatically blackholes all prefixes in 10.0.0.0/8 in the BGP feed, issue the following command:
  /routing filter add prefix=10.0.0.0/8 prefix-length=8-32 set-kernel-type=blackhole chain=myfilter
  /routing filter add prefix=10.0.0.0/8 prefix-length=8-32 set-type=blackhole chain=myfilter


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=====Question: How to filter out the default route from outgoing BGP advertisements?=====
=====Question: How to filter out the default route from outgoing BGP advertisements?=====


Assuming you have a static default route that is redistributed because '''redistribute-static''' parameter is set to '''yes''', do the following:
:Assuming you have a static default route that is redistributed because '''redistribute-static''' parameter is set to '''yes''', do the following:
  /routing filter add chain=myfilter prefix=0.0.0.0/0 action=discard
  /routing filter add chain=myfilter prefix=0.0.0.0/0 action=discard
Then set '''myfilter''' as the out-filter for BGP instance
:Then set '''myfilter''' as the out-filter for BGP instance
  /routing bgp instance set default out-filter=myfilter
  /routing bgp instance set default out-filter=myfilter


[[Category: Routing]]
[[Category: Routing]]

Latest revision as of 15:26, 14 August 2008

Question: How does /ip route check-gateway work?
check-gateway sends pings every 10 seconds. if two successive pings fail, the gateway is considered dead.
Question: How to blackhole a network?
There are two ways to blackhole a network. First, you can do this manually by adding a blackhole route to the routing table, for example, to blackhole a 10.0.0.0/8 network, issue the following command:
/ip route add dst-address=10.0.0.0/8 type=blackhole
Routing filters are the other mean to blackhole a network. To create a routing filter that automatically blackholes all prefixes in 10.0.0.0/8 in the BGP feed, issue the following command:
/routing filter add prefix=10.0.0.0/8 prefix-length=8-32 set-type=blackhole chain=myfilter
Question: How to filter out the default route from outgoing BGP advertisements?
Assuming you have a static default route that is redistributed because redistribute-static parameter is set to yes, do the following:
/routing filter add chain=myfilter prefix=0.0.0.0/0 action=discard
Then set myfilter as the out-filter for BGP instance
/routing bgp instance set default out-filter=myfilter
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