BGP Labs

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BGP Labs

• Avgust Jauk ltjauk_at_arnes.sigt
• ARNES
• Budapest, August 2002

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BGP-4, exercise 1
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ISP-EU
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ISP-B
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ISP-A
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BGP-4, exercise 1 - BGP Stub

• 4 ISPs WG1 ISP-US, WG2 ISP-EU, WG3 ISP-A,
  WG4 ISP-B
• Available address space
• 192.168.lt2group-numbergt.0 for links and PCs
• 192.168.lt2group-number -1gt.0 for loopbacks
• Decide on AS numbers you are going to use
• EU should allocate address space for inter-AS
  links
• Create BGP link between your interconnect router
  and EU.
• After your BGP connection is up, examine your
  routing table. Have any new entries appeared?
• Configure your router to announce (via BGP) your
  local subnets to your peer in EU. Have any new
  entries appeared in your routing table? If so,
  what are the new entries?

4
BGP-4, exercise 1 - BGP Stub

• Break the physical link between your AS and EU.
  How long does it take for the BGP connection to
  go down? How long until the routes learned from
  your BGP peer are removed from your routing
  tables?
• Restore the link. How long does it take before
  all routes are distributed to all routers again?

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BGP-4, exercise 2 - BGP Transit

• EU should become a transit provider by
  configuring its internal routers to pass traffic
  from one customer to another.
• EU must set up an IBGP connection between all
  routers. Use loopback0 address as the
  update-source and next-hop-self!
• What AS paths can you see in the routing table?
  Why?
• Break the link from US to EU. How long does it
  take before all routers in EU detect the link
  failure and remove all US routes from their
  routing tables?
• Try to ping from your PC to the WG2PC3. Does it
  work? If not, why not (try traceroute and examine
  routing tables). What would be the the best
  solution?

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BGP-4, exercise 3
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ISP-EU
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ISP-B
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ISP-A
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BGP-4, exercise 3, Multihomed

• Connect ISP-A and ISP-B to the US.
• ISP-A and ISP-B become multihomed. Check the BGP
  routing tables. Any changes?
• Break the link between ISP-A and EU and ISP-B and
  EU. Do you still have connectivity to EU (or does
  EU have connectivity to ISP-A and ISP-B)? Why
  (not)? If not, solve the problem.
• Restore the links.

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BGP-4, exercise 4
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ISP-EU
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ISP-B
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ISP-A
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BGP-4, exercise 4, Local peering, mutual backup,
...

• Connect ISP-A to ISP-B.
• Do they have a mutual backup to the EU and US, if
  their International links break?
• Take care that they offer backup transit only to
  each other (what if US looses its link to the EU,
  can it still reach EU)?
• Configure
• ISP-A and ISP-B to prefer the connection via EU
  over their direct connection.
• ISP-EU and ISP-US to prefer the connection via
  ISP-A over their direct connection,

10
BGP, exercise 5

• Imagine that your routers cannot cope with the
  full routing (cannot accept all the routes from
  ISP-US). Solution from the US accept only the
  candidate for the default route.
• Inject the default route into your IGP at
  detecting the candidate for the default route.
• Is that solution going to work well in case of
  line breaks?
• If not, how can you improve the set-up?