Questions tagged [bgp]

BGP is Border Gateway Protocol, used on the internet both inside of and in between networks.

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5answers
3k views

Better Enterprise Multihoming

I would like to get some opinions regarding ways in which I can improve a BGP dual-provider, dual-router design. Each provider supplies a /24 public subnet. I will refer to the routers, circuits, ...
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1answer
10k views

Route servers and looking glasses - what are they?

I've heard the term "route server" and "looking glass" thrown around here. What are they, and why should I care?
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5answers
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Why use iBGP inside an Autonomous System, if IGP protocols fulfill the need for internal communication

Can anyone explain why we need iBGP for the routes when we have the IGP protocols (OSPF, RIP) for internal communication within the AS? I have read a lot of articles and books, but I could not find ...
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4answers
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Troubleshooting "Down BGP" connections

Our network experienced a short outage when one of our BGP routes went down for a short time yesterday. Thankfully our connections failed over to our secondary BGP route after a few minutes, and the ...
19
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4answers
6k views

Routing traffic out different links from the same BGP AS

I have two sites, A and B, in BGP AS 65000, and a third site, C, in AS 65001. All three sites have connectivity via carrier MPLS and there is internal connectivity between sites A and B. I am trying ...
18
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3answers
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How does multihoming work with ipv6?

What are the differences between multihoming in IPv4 versus IPv6? Can an enterprise request a provider-independent IPv6 address space from its RIR/LIR which can be advertised to multiple upstream ...
17
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3answers
895 views

Is it possible to remotely influence BGP localpref?

A colleague is attempting to implement active/passive internet multihoming. The design entails sending communities (listed below) to the passive provider to lower the local preference at remote ASes ...
17
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2answers
12k views

In which OSI/TCP-IP model layers do BGP, RIP protocols belong?

We know that in the OSI or TCP-IP model, the higher layer utilizes the services offered by the lower layer. For example, the data link layer uses services offered by the physical layer, network layer ...
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6answers
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Use BGP to defend against a DDoS attack originating from remote AS

I have a question regarding BGP and how to achieve this configuration. My enterprise core router is connected to an ISP (single homed). This router has already exchanged the specific public ip ...
16
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5answers
3k views

How to choose a BGP router ID when using IPv6 only?

Usually, when using BGP, you can choose (or your device chooses four you) a router ID from one of your assigned public IP addresses. Now, let's admit you only run IPv6. As the router ID is still a 32 ...
16
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2answers
10k views

BGP multipath with different ASNs feasible for production networks?

on Cisco (this command is hidden for some reason) #bgp bestpath as-path multipath-relax The default BGP behavior only installs only routes with exact the same AS_PATH into RIB. With multipath-relax, ...
15
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3answers
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Why does BGP RR only reflect the best path?

Can anyone answer why does BGP RR only reflect the best path?
15
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5answers
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When is BGP needed?

I have a question about BGP. When exactly is BGP needed? I remember reading that BGP is needed for communication between autonomous systems, but is this always true? For example, in packet tracer I ...
14
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5answers
2k views

How to filter non-bogon prefixes received via BGP from an Internet Exchange(IXP)?

When connected to an Internet peering exchange(IXP), what is a good way to make sure that people don't send you prefixes that they shouldn't be announcing? With regards to bogons I'm aware of the ...
14
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1answer
2k views

Why BGP implements its own keepalive instead of using tcp keepalive?

BGP doesn't use TCP keepalive, it uses its own keepalive mechanism. My question is why can't bgp turn-on the SO_KEEPaLIVE of TCP and live happily? why does it not use tcp keepalive and implement its ...
14
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2answers
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BGP regular expression .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+

could anyone tell me what ip as-path access-list 100 deny .+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+_.+ stands for?! I searched over the internet for the meaning of this regular expression, but I was unable to ...
14
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2answers
832 views

What is the purpose of BGP TTL security?

What attack vectors does the BGP TTL security knob protect against?
14
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6answers
15k views

Cisco BGP - see communities on advertised-routes?

We have an outbound route-map on an eBGP peer that adds some communities to certain prefixes. Is there any way to prove that this is actually happening from the sender side in classic IOS? show ip ...
13
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6answers
12k views

How does BGP work over TCP?

As far as I know we are using routing protocols to achieve Layer 3 connectivity, I am confused with the fact that BGP works over TCP which is L4. How can L4/TCP be established without prior L3 ...
13
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1answer
2k views

What is the maximum prefix size routed in the IPv6 Internet?

In v4, most of the operators filter BGP updates for prefixes longer than a /24, to preserve the size of the full view. What about IPv6 ? Is there such "convention" that stands out ?
13
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2answers
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VPLS Multihoming on Junos - FEC confusion‏

I'm going over the VPLS multihoming options on Juniper's web site. I'm not concerned with LAG and MC-LAG for the moment. As far as I'm aware: FEC128 is when you are using manual discovery of ...
12
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1answer
5k views

Is it possible to connect two private eBGP peers with the same AS number?

The Problem A third party has implemented a small network and private BGP setup within one of our branches. We need to setup a eBGP peer relationship with this network. However we are both using the ...
11
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3answers
786 views

Circular BGP propagation

This one is a difficult to describe, it's hypothetical because I'm learning about routing and right now I'm focused on BGP. Let's say my ASN is 65000, and I announce 192.0.2.0/24. My peer, AS 65001 ...
11
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1answer
3k views

After TCP is established which BGP peer will send open message first?

After a Tcp connection is established between two bgp peers. which peer will send the open message first ? the active peer(which is initiating outbound connection) or the passive peer?(peer which is ...
11
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1answer
12k views

How is BGP "AS_SET" used?

RFC 1771 defines a path attribute type of AS_PATH as follows: AS_PATH (Type Code 2): AS_PATH is a well-known mandatory attribute that is composed of a sequence of AS path segments. Each AS path ...
11
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2answers
800 views

BGP Prefix Announcement Issue

I'm having a weird issue. Here is the setup. We have 2 Foundry SX's. SX01 ---> ISPA | | SX02 ---> ISPB I have a /24 from ISPA and another /24 from ISPB. Both /24's are able to be ...
11
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3answers
1k views

Quagga routing and security

I have a quagga router with two transit neighbors and announcing my own IP space. I recently joined a public peering exchange (IXP) and so I'm part of their local network (/24), together with all ...
11
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1answer
813 views

How can I check to see if I am receiving MED's?

I have a BGP session with a transit provider in two different cities. We are both using the same AS at both locations. I am expecting them to be sending me MED's for me to use for routing decisions ...
10
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3answers
1k views

Does anycast addressing add additional latency in any way?

Does anycast addressing, in itself, add any additional latency to network connections? Specifically, if you had two servers located in the same data center that had extremely similar routes/number of ...
10
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4answers
3k views

Embedded routers vs. software routers in the datacentre

I've been looking for a new 'core' router to put in our new rack which is colo'd at a nearby datacentre. What I've come across is the usual Cisco/Juniper/Brocade lineup, with the usual unattractive ...
10
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3answers
4k views

Inbound BGP load-balancing from same ISP router

I have two BGP routers for DIA with an issue with one provider in that the two links to this provider land on the same SP router. My ethernet handoffs via two separate MetroE links from another ...
10
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2answers
2k views

Why does my Cisco 6509 BGP table use two entries in my TCAM?

I have a problem on my Cisco 6509, each entry in my BGP table occupies two entries in the TCAM. If I show capacity forwarding, I see MPLS entries in L3 forwarding resources. But, I do not use MPLS on ...
10
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2answers
5k views

load balance between two ISP bgp links

I have up-links to two separate ISPs on one router and receive a default route from each via BGP. Both links are the same speed and BGP is used only to advertise our prefixes out. Whats the best way ...
10
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7answers
3k views

Only One Path in the Looking Glass

I understand that only the best path is advertised to eBGP neighbors, but is this true of iBGP? If I peer with two providers, I was under the impression that anyone else peering with both of my ...
10
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1answer
5k views

How would one route an IP network through different ISPs?

So, if I have a site that has 2 (or more) internet connections, with a routable IP subnet that I own, and one ISP goes down, how do I tell the rest of the world to send traffic addressed to my network ...
10
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1answer
261 views

Unexpected AS-PATH ACL behavior

4 routers, lab environment. Trying to filter out routes originating from AS2 (not that leverage AS2 as transit). The process I've followed is: Bakers#sh ip bgp regex _2_ BGP table version is 41, ...
9
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3answers
2k views

How can I calculate the number of internet routes myself?

In the JNCIA study guide, it is stated that there are currently 120k routes on the internet and that Juniper supported up to 450k. How did they arrive at the 120k? If I wanted to know how many exact ...
9
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3answers
19k views

OSPF or iBGP for interior routing protocol?

So the plan is, two core routers each with a eBGP session to one of two ISPs with full routes. Both routers publish their full tables to each other so they can control traffic flow more intelligently ...
9
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2answers
2k views

BGP Autonomous System Path Duplicate AS

Is it normal to see a path as such in my BGP update ? 12 34 33 2 2 45 331 As I can see from the path above, AS number "2" appears twice ! Is it normal ? Are they any scenarios that could have made ...
9
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2answers
20k views

Learned eBGP routes not distributed to iBGP neighbors

I have (in GNS3) three Cisco 3640s running 12.4(23) connected in series (R1 -> R2 -> R3). R1 and R2 are eBGP peers, R2 and R3 are iBGP peers. R1 advertises network 192.168.1.0/24. R2 receives this ...
9
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2answers
6k views

Should I use default routes or full BGP table?

I have a network with three links (ISPA, 3MB, ISPB, 1.5MB, ISPC, 50MB). I have three different speeds, and as such, ISPs A and B are primarily used for redundancy. I'm currently receiving routes from ...
9
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2answers
501 views

How to handle performance degradation deep in your provider's network?

What are some possible ways to detect packet loss deep in a provider's network that is several hops away? With multiple providers peered over BGP on our Internet edge routers, I need to be able to ...
9
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3answers
18k views

ASR1K feature licensing navigation

I'm looking at deploying a pair of ASR1001 units at the WAN edge to support 2x IP Transit and 1x Peering services. I need to do IPV4 and IPV6 eBGP and iBGP to advertise the peering routes into the ...
9
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2answers
10k views

BGP remote-triggered blackhole (RTBH) filter for Juniper

I'm trying to find the most elegant way to implement a RTBH filter for routes received from a customer. The filter should: Only accept the customers own prefixes from a prefix-list Only accept /32 ...
9
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1answer
4k views

How to run redundant BGP via Quagga on /30 netblock?

My new BGP upstream has allocated a IPv4 /30 netblock as the glue block for connecting our routers. I however want to run two routers, and failover between them. If the netblock was larger (/29), I ...
9
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1answer
2k views

How much RAM you actually need to keep whole global BGP routing table?

It seems that different sources claim very different RAM consumption for having whole BGP routing table information in RAM and having the router to correctly route the traffic. According to ...
8
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3answers
8k views

Why are iBGP routes not propagated to other iBGP neighbors?

I have been searching this on the web. It is generally expressed as by default, iBGP does not propagate routes learned via other iBGP neighbors. I am trying to understand the underlying reason. The ...
8
votes
1answer
2k views

Does RIP to BGP redistribution for an MPLS VPN make sense?

A customer was recently adamant to perform redistribution of their RIPv2 routes into BGP. This is over a standard MPLS VPN solution whereby the CE routers are fully managed. This approach feels ...
8
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3answers
6k views

BGP - Soft Reset Outbound & Verification

My understanding of the command: clear ip bgp * soft out is that the router on which the command is issued will re-advertise everything it knows about BGP to it's neighbors. As I see it, it's as if ...
8
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3answers
7k views

Active / Active BGP with Default routes

I've just lodged a request with upstream to clarify some specifics of their recommended BGP configuration. Currently, I will be dual-homing with my upstream via PI addresses. Advertising via BGP with ...

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