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FAQ
Index:
Questions and Answers:
Q. What is BGP?
A.
The Border Gateway Protocol (BGP) is an exterior routing protocol. BGP version
4, described in RFC 1771, and further defined in version 5 of the BGP4 Internet
Draft of January 1997, was designed for routing between Autonomous Systems. BGP
Autonomous System Confederations information can be found in RFC 1965. BGP Route
Reflection information can be found in RFC 1966. The BGP COMMUNITIES attribute
is described in RFC1997. Although it can be used internally, BGP is primarily
used to route between networks, rather within them (such as RIP, OSPF, IS-IS).
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Q. What is multi-homing?
A. "Multi-homing"
means having multiple connections to the Internet. There are two basic types of
multi-homed organizations:
- An organization which
has connections to provider at more than one point of presence, and has internal
links between these sites; or
- An organization which has a connection
to provider and at least one other Internet access provider.
If
you have only a single connection to the Internet there is not a lot to be gained
from using BGP. With only one gateway, your router already knows how to send all
traffic not destined to one of your networks. Everyone should be conscious of
keeping the Internet's routing table as small as possible. This can be best addressed
by aggregating addresses using CIDR blocks. As a single-homed connection, your
provider will likely choose to aggregate your networks with the networks of other
single-homed customers and thus announce a single CIDR block under their ASN in
order to reduce the routing table size.
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Q. What are the benefits of
using BGP?
A.
The single word answer is "control". When you decided to multi-home it was for
a reason, maybe extra capacity, redundancy, or tariffing, so in order to actually
perform any of these functions you need to control how your networks are announced
to your providers. If you don't exchange routes with them but rely on them announcing
your routes you could find your traffic flowing down an expensive low capacity
link with the other cheaper, higher capacity links mostly idle!
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Q. Does using BGP make it easier
to change providers?
A.
Each Tier 1 backbone provider has its own procedures to handle customers that
wish to use BGP. These procedures may be easier than the procedures used for staticly-routed
customers, but generally each will require some sort of route registration, so
there is no real time or effort saved.
However if you are using BGP
to more than one provider, you can migrate routes between the providers without
their intervention (assuming any route registration has already been performed).
In order to migrate the routes, you should start announcing the routes to the
new provider and confirm that the new path is visible via a "looking glass". You
may need to prepend your AS on the old path to make that path "longer". Having
confirmed that the new provider is successfully announcing the routes you can
then terminate the announcement to the old provider.
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Q. Do I have to use BGP with all of my upstream providers?
A.
For the best results, you will find it advantageous to use BGP, but it isn't strictly
necessary. In theory, your routes should originate from the same AS number, so
you should announce your routes via BGP even if you don't listen to all announcements
being sent to you. For example, you could use a static route to default to a provider
rather than accept the routes they are sending via BGP.
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Q. Where can I get an Autonomous
System Number?
A.
You can get an Autonomous Number from The American Registry for Internet Numbers
(ARIN). ARIN is a non-profit organization established for the purpose of administration
and registration of Internet Protocol (IP)numbers to the geographical areas previously
managed by Network Solutions, Inc. (InterNIC). The URL for ARIN's Registration
Services is http://www.arin.net/regserv.html
One of the following conditions must be satisfied before receiving an
Autonomous System Number:
- Unique Routing Policy:
Please explain how your routing policy is different from your provider.
- Multi-homed Site: If your organization is currently multi-homed,
please explain exactly how you are connected to the Internet. Please include the
gateway protocol used, the IP network addresses that make up your AS, and technical
point of contact information of your upstream providers/peers. The point of contact
information must include full name, and email address for verification.
The
URL for the Autonomous System Number application form is http://www.arin.net/regserv/templates/asntemplate.txt.
For a complete list of all registered ASes on the Internet, see this
link: ftp://rs.arin.net/netinfo/asn.txt.
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Q. What is the Network Layer
Reachability Information (NLRI)?
A.
Sets of destinations are the Network Layer Reachability Information (NLRI). A
destination is a network address prefix, with a prefix length. For example, the
NLRI for the private network 192.168.20.0 would be 192.168.20.0/24.
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Q. What is a BGP route?
A. The combined
bundle of a path to a destination Autonomous System, the attributes of the path
used to reach the Autonomous System, and the NLRI located at that Autonomous System
is called a BGP route.
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Q. What ImageStream routers
support BGP4 and how much memory do they require?
A. All Pro Series
routers, as well as the Rebel, Gateway and Enterprise Routers in the Industrial
Series support BGP4. All of these products require 128MB of memory in order to
run BGP4 and receive full routing views.
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Q. How can I tell if BGP4 is
enabled on my ImageStream router?
A.
Use the Configuration and Update Menu:
- At the
Login: prompt, enter root.
- At the Password: prompt, enter your
password.
- Choose Option 1 (Configuration and Update Menu) from
the Main Menu. Select Option 3 (Service Configuration).
- From
the Service Configuration menu, you can see the status of the Dynamic routing
(gated) package. If gated is running, the option will show "(running)". Conversely,
if gated is not currently running, the menu option will display "(stopped)".
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Q. How can I enable BGP4 on
the router?
A.
Use the Configuration and Update Menu:
- At the
Login: prompt, enter root.
- At the Password: prompt, enter your
password.
- Choose Option 1 (Configuration and Update Menu) from
the Main Menu. Select Option 3 (Service Configuration).
- From
the Service Configuration menu, you can see the status of the Dynamic routing
(gated) package. If gated is running, the option will show "(running)".
- To
start gated, choose Option 3 (Dynamic routing) and choose Option 5 (Start gated)
from the Dynamic routing menu. You will also want to select Option 3 (Enable gated
on boot) to ensure that BGP session will be established at boottime. Ensure that
you have configured gated prior to attempting to start it. Unless it is properly
configured, gated will not start.
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Q. What is the best source
of information about configuring BGP4?
A.
The BGP Routing Protocol page on the ImageStream
Technical Support site or in the individual gated configuration files on the router.
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Q. Why must all BGP peers in
an Autonomous System be peered with each other?
A. A fundamental
rule of BGP is that all internal peers in the same Autonomous System must all
fully talk to each other. That is:
- If you have
peers, A, B, C in an Autonomous System, then there has to be three peers: An A/B
peer, a B/C peer, and an A/C peer. Add a fourth, D, and then you need A/D, B/D,
and C/D peers.
- The point being, from the BGP spec: If a
router B, learns a route (path attributes + destination) from internal peer A,
it _assumes_ that all other internal peers hear it too, so it won't forward the
information onto any other internal peer. It is possible to sidestep this requirement
through the use of either BGP route reflectors or BGP confederations.
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Q. What is used as the BGP
Router ID on ImageStream routers?
A.
The IP address of the Ethernet0 interface is typically used. But the router will
not assume this; it must be explicitly set in the BGP configuration file (gated.bgp).
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Q. Do I need to define my static routes in my interface
configuration file (wan.conf) and in the main gated configuration
file (gated.conf)?
A.
Yes, you must specify any static routes in both places. If you do not specify
the static routes in the main gated configuration file (gated.conf), gated will
remove those routes from the routing table at runtime.
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Q. How long must a route exist
before BGP will forward it?
A.
A route must exist for 30 seconds before BGP will forward it.
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Q. In the route precedence,
where are Local routes in the precedence?
A. Local (directly connected)
routes are the most highly preferred routes, with static routes being the next
highly preferred. Route precedence can be adjusted within the configuration by
changing the preferences on different route types.
Local (Direct) routes>Static
routes>Dynamic routes
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Q. What third-party products
are interoperable with BGP4 on an ImageStream router?
A. ImageStream's
BGP4 implementation has been tested for interoperability with the following products,
among others:
- Cisco IOS
- Nortel/Bay
Networks OS
- Juniper Networks OS
- gated public
and commercial versions
- zebra
Any
RFC-compliant BGP4 equipment should interoperate with ImageStream routers. Please
contact ImageStream Technical Support if you have BGP interoperability questions
with specific equipment.
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