Dongkee LEE ([email protected]) 1 BorderGuard: Detecting Cold Potatoes from Peers Nick Feamster,...

Dongkee LEE ([email protected]) 1

BorderGuard:BorderGuard:Detecting Cold Potatoes from PeersDetecting Cold Potatoes from Peers

Nick Feamster, et al.


Overview.Overview.

Hot/Cold Potatoes.

BoarderGuard.

Results.


Hot potato routingHot potato routing

Peering contracts typically require the peer to provide consistent routes at all interconnection points.

AS B can direct traffic through

peering point 3.


What’s the best route?What’s the best route?

BGP decision process.

1. Highest local preference.2. Lowest AS path length.3. Lowest origin type.4. Lowest MED (with same next-hop AS). 5. eBGP-learned over iBGP-learned.6. Lowest intradomain path cost to egress point.7. Lowest router ID of BGP speaker.


Using eBGP Feeds Using eBGP Feeds A network has m peer ASes, p = 1 … m

and np eBGP sessions with peer p. rp,u – route for the prefix d determined by update message on se

ssion u, where u in [1, np]

AS p

Let’s go to AS p

We can choose one of the rp,1 … rp,np

321

rp,1 rp,2 rp,3 rp,np ...

np


Using eBGP Feeds Using eBGP Feeds Upon receiving an update messages on session u,

Compare λ(rp,u) to λ(rp,v) for v in [1, np],

where λ() is a route ranking function.


Using iBGP Feeds Using iBGP Feeds Routers(p) - set of np routers in the AS that peer with p. For each border router i,

Import policy Ii is applied to rp,i

Select the best route bi = Ii (rp,i) for a destination.

Distributes the route bi to other routers in the AS via iBGP.

Limitations,


Using iBGP Feeds - LimitationsUsing iBGP Feeds - Limitations Import policy can make consistent routes appear inconsistent. Inability to distinguish inconsistent routes from a missing route.

AS p

21

AS q

“1 4 3” “1 5 3”

Monitoring point

b1 b2

λ(rp,1) = λ(rp,2)

Ii (rp,1) is not Ii (rp,2)

b1 = Ii (rq,1)


Using iBGP Feeds Using iBGP Feeds Upon receiving an update messages on session u,

for each border router i, i in [1, k] :

for each router j in Routers( peer(bi)) :

compare λ(bj) to λ(Ij ( I-1i(bi) ))

λ(rp,u) = λ(rp,v)

λ (I-1u (bi)) = λ(rp,v)

λ (Ij(I-1u (bi))) = λ (Ii(rp, v))


Results Results

AT&T’s commercial IP backbone. Analyze eBGP from one of AT&T’s peers.

iBGP from the border routers in AT&T’s net.

Assumes that AT&T’s import policies and peering sessions did not change during this period.


How bad routes can come … How bad routes can come … How bad routes can come from good peers ?


The END

Dongkee LEE ([email protected]) 1 BorderGuard: Detecting Cold Potatoes from Peers Nick Feamster,...

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