Session 3: BGP

Question 1

What does BGP stand for?

Answer 1

Border Gateway Protocol

Question 2

Why is this protocol unique?

Answer 2

This is the only protocol for interconnecting networks at the global level that is in use on the internet.

Question 3

What type of protocol is the BGP?

Answer 3

Exterior Gateway Protocol

Question 4

What is BGP typically referred to when used in the administrative domain?

Answer 4

IBGP

Question 5

What does IBGP stand for?

Answer 5

Internal Border Gateway Protocol

Question 6

What is IBGP’s main usage?

Answer 6

Provide information to the internal routers

Question 7

What does EBGP stand for?

Answer 7

External Border Gateway Protocol

Question 8

What is EBGP’s main usage?

Answer 8

The interconnection of networks on the internet or other external bodies.

Question 9

What objectives does the IBGP need to fulfill?

Answer 9

Disseminate internal routing information
Originate and aggregate address prefixes
Announce prefixes to other domains/AS
Tag prefixes with routing information
Receive information from other networks/AS
Receive and choose (filter) between external prefixes
Transfer information through internal routing domain
Received information from one domain may be transferred (and possibly
modified) to other domains

Question 10

What are the BGP high level objectives?

Answer 10

Routing protocols studied so far have different issues:
Distance vector algorithms suffer from potential non-convergence
(Bellman-Ford)
Link-state algorithms may not use the same metrics on all routers,
which would result in loops
LS algorithms also do not quite scale: The LS database would be far
too large were millions of routers to be included

Question 11

What is the other important consideration not addressed by DV or LS protocols?

Answer 11

policy: Commercial relationships and cost are difficult to capture by link costs

Question 12

Why is the foregoing question important to consider for BGP?

Answer 12

Link costs may be asymmetrical

BGP is a policy-based routing protocol, and is designed around a destination-based forwarding model

Other relations such as origins, link load, or type of service are not
addressed explicitly

Provides a toolkit for expressing and enforcing AS-level policy
decisions

Question 13

What must BGP interact with?

Answer 13

The internal routing protocols of each AS

Question 14

What will I-BGP typically operate in parallel with and why?

Answer 14

Another IGP to form forwarding tables.

Question 15

What are BGP challenges?

Answer 15

Configuring policies is not straightforward
Route flapping
Long AS path criteria result in DV-like behaviour and bouncing
As with DV, PV is not guaranteed to converge
Scalability is a constant concern
Performance is not optimal: BGP does not explicitly allow to balance load across multiple paths

Question 16

What are some BGP security concerns?

Answer 16

BGP communication normally will run over unprotected TCP sessions

Beyond straightforward TCP manipulation, messages can be manipulated
to alter routing policy communication and BGP attributes

Question 17

What are some BGP security challenges related to monitoring and defensive filtering?

Answer 17

BGP speakers can aggressively filter out some announcements and modify others

Attacks such as prefix hijackings are difficult to detect

Question 18

What is “fat fingers”?

Answer 18

Related to the leaking of prefixes and the misuse of these.

Question 19

What is the BGPsec_Path and what does it consist of?

Answer 19

It is an attribute that is non-transitive and consists of the secure path and a signature block.

Question 20

What is included in the signature blocks?

Answer 20

All the previous signatures in the sequence.

Question 21

Who can use the BGPsec attributes?

Answer 21

Only BGPsec-speaking

neighbours.