20
votes
Accepted
Does anycast addressing add additional latency in any way?
Does anycast addressing, in itself, add any additional latency to
network connections?
No.
one using unicast and the other using anycast
Anycast is unicast. It is just that the same network is ...
- 98.8k
18
votes
Accepted
Can I announce prefix 161.117.25.0/24 even though I don't have all of /24 IPs?
That /24 is part of a larger block (161.117.0.0/16) which is assigned to Alibabacom Singapore and announced by AS45102 (which is Alibaba again). My guess is that you're a customer of them and have ...
- 17.1k
16
votes
Accepted
In which OSI/TCP-IP model layers do BGP, RIP protocols belong?
You have to remember that models like OSI are just that, models. They are theoretical. The real world doesn't fall neatly into these models. For the most part, routing is a layer-3 function, but, as ...
- 98.8k
12
votes
Accepted
Difference between default route, partial and full routing table for a BGP session
A default route is the route that will be used if there's no other route that matches the destination in the router's forwarding table.
A full routing table is a table which contain all the routes the ...
- 19.5k
11
votes
Accepted
Why do IXPs need ASN?
In its most basic form, an IXP is nothing more than a large switch, allowing many networks to exchange traffic without having to interconnect with every other network on the IXP, thus reducing costs ...
- 17.1k
10
votes
Accepted
Smallest IPv6 block advertised?
Yes. Nobody will advertise any network smaller than a /48. The same thing is in IPv4; no ISP will advertise any network smaller than a /24.
The problem is the sheer number of routes that would ...
- 98.8k
9
votes
Accepted
Why is the BGP base on TCP 1027 rather than 179?
One side of the connection will have an arbitrary port number, the other will be on 179.
Cisco Press "BGP Fundamentals" has a good explanation (link)
the neighbor with the higher IP address ...
- 16.2k
9
votes
BGP traffic management
Load balancing with BGP is very tricky and the mechanisms available are quite crude. With BGP you can only route based on the destination IP address. There's no way to distinguish payload traffic and ...
- 17.1k
8
votes
In which OSI/TCP-IP model layers do BGP, RIP protocols belong?
BGP is on top of TCP, so it would be Internet layer 4, OSI layer 7. Usually external BGP is done only between 2 directly connected peers, enforced by setting TTL flag on IP header, which is located at ...
- 656
8
votes
Accepted
Why does iBGP require a full-mesh?
...why is a iBGP connection between two routers that don't have eBGP
connections needed? They won't distribute anything, right?
Not quite right. It's not that two routers connected via iBGP cannot ...
- 98.8k
8
votes
Accepted
RTBH vs FlowSpec
Typically, FlowSpec is only used within a specific network, while RTBH is used between a network and its upstream(s). The mains reasons for this are that
only a few vendors support FlowSpec
allowing ...
- 17.1k
8
votes
Accepted
What considerations should be made when determining whether to use the BGP "network" command vs Redistribution?
First - there are two distinctly different problems being solved with these commands:
The network and redistribute commands are mechanisms to initiate routes into BGP, either statically (with a ...
- 6,104
8
votes
Difference between default route, partial and full routing table for a BGP session
A default route is the same in every routing table -- it is the route of last resort, when no other route matches.
Since many organizations have only a single connection to the Internet, a default ...
- 67.1k
8
votes
Accepted
My BGP router does not advertise configured prefixes
Router 2 will not advertise networks that are not in its routing table. So if router 2 does not have a route to 2.0.0.0, it will not advertise it. This prevents BGP routers from
"blackholing" ...
- 67.1k
8
votes
Accepted
BGP Best Path Selection Algorithm
By default, the shortest path will be the best path. If you notice, the first three are locally configured options that you can use to override any selections that would normally be made by the ...
- 98.8k
8
votes
Accepted
How much RAM you actually need to keep whole global BGP routing table?
Here is the info given but a production router that does IPv4 BGP only, as of 2021 October 5:
1547576 RIB nodes, using 142 MiB of memory
1687609 BGP routes, using 103 MiB of memory
8 Static routes, ...
- 19.5k
8
votes
Accepted
In practice, how are BGP Advertisement destinations determined and configured?
Some connection between the two ISPs is needed. Dedicated fibers (for example in a datacenter they're both present in) is very common. But there are other possibilities: a layer 2 connection (for ...
- 17.1k
7
votes
How outdated are BGP books?
A good way to find the differences is to look at the RFCs.
At the time a book published in 2000 was authored, the current version of BGP would have been according to the 1995 version of the standard: ...
- 591
7
votes
Accepted
Prefix hijacked by another ISP
At this moment, there's not that much that ISP's can do to prevent these kind of hijacks except, as you said, doing proper filtering of received and announced prefixes. Unfortunately many ISP's still ...
- 17.1k
7
votes
Accepted
BGP null route when DDoS?
The only answer we can give you is 'talk to your ISP'. Remotely triggered blackholing (RTBH) is an often used technique, but we can't tell if your ISP supports this.
When using RTBH, you can announce ...
- 17.1k
7
votes
Accepted
Why is MBGP needed?
MBGP or Multiprotocol BGP extensions
The first BGP specification was published in 1989, well before IPv6 was created and only shortly after multicast was added to IPv4. Even BGP-4 doesn’t support IPv6,...
- 166
7
votes
Accepted
Best practice for advertising routes in BGP
You are conflating two different issues:
Route-maps can act as a policy filter, selecting which prefixes are advertised to neighbors and which are accepted from neighbors. Advertise-maps allow you ...
- 67.1k
7
votes
Accepted
Why are iBGP routes not propagated to other iBGP neighbors?
The reason is to prevent routing loops. BGP routers don't advertise routes learned from iBGP neighbor A on to a second iBGP neighbor C. This is specified in the BGP RFC 4271 §9.2 paragraph 2. To ...
- 98.8k
7
votes
Accepted
How is traffic forwarded though IXPs if route servers do not forward any traffic
In the IXP, the routers still have connections to each other, so traffic is sent between the routers. You may be confusing the (logical) TCP connections used by BGP to exchange routing information ...
- 98.8k
7
votes
Why Cisco BGP neighbor command need the remote-as number?
cisco documentation says that:
"the configuration does not overtly define peers as iBGP or eBGP. Instead, each router examines its own ASN as defined in the router bgp command, and compares that value ...
- 71
7
votes
BGP convergence issue
There are two issues here:
BGP keepalives are 60 seconds, and the hold down timer is 3 times that. So that's your lower limit, unless you work with your carrier and adjust your timers. You both ...
- 67.1k
7
votes
BGP | Advertise a summary prefix out to customer location
This appears to be a Cisco router. Cisco has the aggregate-address command.
You can advertise the aggregate address and all the individual addresses:
aggregate-address 8.0.0.0 255.0.0.0
or only the ...
- 98.8k
7
votes
Accepted
How to block advertisement of a prefixes recieved from 1 BGP neighbor to another
As mentioned by Ron, you can use no-export (Don't advertise to any eBGP peers) or no-advertise (Don't advertise to iBGP or eBGP peers) to achieve this. However, this may strain scalability issues if ...
- 1,307
Only top scored, non community-wiki answers of a minimum length are eligible