Questions tagged [bgp]

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

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Are eBGP networks automatically advertised to iBGP?

as the title says, I am working with a rather simple topology: R1<--eBGP-->R2<--iBGP-->R3 R1 has an eBGP neighborship with R2. I recently added an iBGP session between R2 and R3 (both are ...
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BGP: Are Virtual Internet Exchanges more efficient than normal internet transit?

There are a number of virtual internet exchanges that BGP peer over VPN links when local presence is not available. Given the IP encapsulation overhead, and the fact that these routes still cross the ...
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cisco BGP command: network without mask

My topo is as follows, following is my configuration, although bgp command network is without mask, it could advertise classful address 10.0.0.0 R1#show ip route Codes: L - local, C - connected, S - ...
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Does an official list of tier 1 ISPs exist?

I'm trying to find an official list of tier 1 ISPs. I found a list on Wikipedia but can't quite understand how it was compiled, it just lists AS rank as a source. I also found some other websites that ...
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How can I have multiple servers and IPs if I only have 1 ip with gigabit connection?

I have 1 gigabit connection with static public IP address... Without depending on my local ISPs colaboration, is it possible to buy IPs from an online service and route each individual IP to my local ...
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How can I implement BGP between two routers that have already been configured with different routing protocols?

I have two different AS with different IP ranges and subnets, and the first router stack is running RIP, and the second one is OSPF. I want to configure BGP between "Router-PT Router23" and &...
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BGP configuration multi-hop ping not working

I'm learning bgp and studying on a simple lab I'm unable to ping a loop0 two hops away while the loop0 on the nex-hop router is reachable Topology is simple R3-R1-R2, from R2 i'm able to ping loop0 on ...
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How to determine a BGP node's IP address

Let's say you do a traceroute scan to a network that is far away, and there a lot of intermediate hops, how do you know which one belongs to a BGP node, and which one is part of the target server? Let'...
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How to understand BGP Announcements on Cloudflare Radar?

See the "BGP Announcements" card on any AS page. Example: https://radar.cloudflare.com/routing/AS13335 I fail to reproduce the same numbers with my own tool when I use a single location from ...
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How can we use "source port randomization" in BGP?

I wonder if we can change the default port TCP port number(179) used during the BGP session. I recently came across a document BGP Vulnerability Testing: Separating Fact from FUD. It suggested ...
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Why CDN ASes are not shown in BGPreader?

I am using bgpreader as bgpreader -A "20940" -w 2023-7-28,2023-7-31 where ASN 20940 is Akamai (a CDN). I wanted to view RIB, updates involving this ASN. I couldn't find the result for other ...
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Juniper - ECMP with BGP

As I know, with the command "multipath" BGP can install more than 1 route to a specific destination into the routing table. IE.: 1.1.1.1 --> 192.168.0.2 1.1.1.1 --> 192.168.0.5 But ...
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BGP Convergence Design Question

i read that good convergence method for BGP is to rely on IGP Convergence by declaring next-hop dead and not decreasing BGP timers because the latter will cause unstable network. i really fail to see ...
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Difference between internet path and AS path

As per my understanding, the Internet is the interconnection of ASes where BGP is a kind of "glue". BGP carries routing information from one AS to another. Also, the AS path is one of the ...
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Can control plane and data plane be different in BGP?

I have heard that the BGP routes exchanged between the routers do not necessarily mean that the actual data path will follow the specified routes. How can the data path and control path be different ...
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The Use of BGP Communities

I am studying BGP communities at the moment. I understand that communities are path attributes which are a way of tagging specific BGP route advertisements in order to ensure proper route selection ...
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Advertising IP prefixes to the internet using BGP

I am studying BGP at the moment. From what I've learned, in order to participate in routing on the internet and use BGP, we need to register a public provider-independent IP address block and a public ...
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The Atomic Aggregate Attribute in BGP

I am trying to understand how the Atomic Aggregate attribute works in BGP. So if my understanding is correct, once we configure route summarization, the path attributes of those routes that we've ...
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iBGP Confusion - Clarification Needed

Sorry if this is an XY problem -- struggling to understand a few concepts. To put it simply, I just don't understand when iBGP is needed. Been reading the CCNP Enterprise - Core and the example ...
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MED versus AS Path Prepending for inbound path manipulation

I am currently studying about the BGP path selection process and I came across MED and AS Path Prepending which can both be used to affect how traffic enters our network. Are there any scenarios where ...
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Confused about the BGP ConnectRetryTimer

I am studying about BGP adjacencies at the moment. About the Idle state. I've read from my Cisco book that errors can cause the neighbor state to revert back to Idle and the ConnectRetryTimer is set ...
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Traffic Flow From the Customer Through the ISP

I am currently learning about BGP at the moment and I have a question about the traffic flow and redistribution. So ISPs typically run some sort of IGP within their AS. If I was to send a packet to ...
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How do ISPs ensure that the IP block that is being advertised to them is valid?

Consider the following situation where we have a customer that is connected to two ISPs for redundancy Let's say that this customer has its own IP address space that it wants to advertise to those ...
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BGP and Multi-Hop Adjacencies Using TCP

I am studying the basics of BGP and my book states the following: "BGP sessions use TCP port 179. TCP allows for adjacencies that are multiple hops away" I understand that this allows ...
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What is the use of private ASNs?

I am currently studying BGP at the moment. The public ASNs that are assigned to ISPs and larger organizations that want to participate in routing on the internet make perfect sense to me. However, I'...
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EIGRP AS versus BGP AS

I am currently studying the basics of BGP and I am very early into this topic. So with EIGRP, I was told that an AS is basically a collection of routers/a routing domain that is under a single ...
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BGP: What are the considerations for announcing a RIPE block in ARIN-controlled territory?

We have an ASN and are considering leasing a addresses under RIPE's jurisdiction (because they cost less). However, we are in North America and would announce those addresses via BGP to our providers ...
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Interior vs Exterior Gateway Protocols

I'm new to Networking and I was reading about the Interior and Exterior Gateway Protocols ,but i couldn't understand some points , as stated in a reference: IGPs are designed to work in private ...
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Is the security of BGP using a pre-shared key dependent on the security of MD5?

The german wikipedia article to BGP states (translated): In the basic configuration, a BGP-Router is susceptible to spoofig attacks, through which the attacker can manipulate the routers. By using an ...
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Allow active connections in firewall on multiple BGP connected routers

We have a network on its own AS with 2 routers connected to 2 AS via BGP (full routes). The routers also both have a firewall on board that by default drops all traffic, except the one allowed. We ...
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Why are BGP tables suddenly filled with IPv4 routes?

According to article I looked at, bgp routing tables are approaching a maximum size and this is linked to IPv4 exhaustion. Why is this problematic and what is the cause? Will this be a problem with ...
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Why do typical spine-leaf architectures have one border leaf instead of all leafs having an uplink?

In all spine leaf architecture explainers I've seen I've come across the concept of the border leaf which is used as the connection point of the entire clos network to an upstream router, be it either ...
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How Network layer routing actually works in the physical world

This is my first question here, It might be a vague or off topic, I apologise in advance, but I am happy to improve it Basically I have a somewhat decent theoretical understanding of the OSI model. ...
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BGP outbound traffic engineering in multi-homed network with 2 ISP's

I have network with switches at access layer and 3 host networks, 2 core routers , 2 border routers , that have iBGP connection with each other and ospf with other 2 core routers, also each of them ...
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Can you have multiple paths in BGP through different ASes?

In a course about networks in my university, we learnt about how in BGP routes, each AS chooses a single route to each IP prefix (though you may have multiple iBGP routes). Meaning that in the ...
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The relationship between IP address and AS number

I've recently been looking for the IP prefixes originating from a specific AS. And there are a few questions I'd like to get confirmed. We can register IP addresses and ASN from RIR. But where can we ...
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Possibility of transferring data over the same-level networks, rather than the higher-level network

This is a silly(maybe interesting) question. Assume four ASes are connecting to the Tier 1 network(A, B, C and D). B is peering with C and D. A is close to B, but too far from C and D to make peering. ...
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The relationship between AS upstreams, downstreams and peers

I find AS1221 is both the upstream and the peer of AS13445 from ipinfo.io/AS13445. However, as far as I know, there is no upstream or downstream relationship when talking about peering. Is anything ...
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Are there any ASNs with 0 IP addresses? [duplicate]

Here is the list of all the US ASNs networks ranked by the number of IP addresses: https://ipinfo.io/countries/us However in the page 10, I can see some ASNs with 0 IP addresses: https://ipinfo.io/...
Loresim's user avatar
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how can you establish an (e.g.) IPsec tunnel with Cloudflare, when they announce your IP range via BGP?

I've looked into Cloudflare's "Magic Transit" and I do understand the basic concept of it. However, I do not understand why it would ever work that Cloudflare could return traffic to you (...
BlackFlag's user avatar
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Unable to configure BGP on Arista DCS-7048T-A

I am, admittedly, rather lacking in networking knowledge. However, I managed to learn quite a lot of server and development skills through trial & error and by asking various people/forums. I hope ...
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IP subnet with extra information outside of BGP and RIPE database

I'm trying to look into the sources of some whois services that can provide more information than BGP and RIPE databases. Example: If I lookup the IP 104.234.88.128 in https://whoer.net/checkwhois I ...
felartu's user avatar
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How to handle route conflict between two routers?

I am learning about route protocols and I would like to know what is the common approach to handle route conflict between two datacenter. I have the scenario bellow: So I want devices on DC1 to ...
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Is BGP always required when you have multiple ISPs?

I am trying to understand when is Border Gateway Protocol needed and I stumbled upon this question: When is BGP needed? The chosen best answer says: You could peer with your service provider and ...
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Can a BGP speaker records alternative paths to the same destination?

The BGP RFC 4271 reads : In the context of this document, we assume that a BGP speaker advertises to its peers only those routes that it uses itself (in this context, a BGP speaker is said to "...
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What are any disadvantages of redistributing eBGP routes into IGP

I wonder if there are any conceptual disadvantages of redistributing routes learned through eBGP peerings into an IGP, like OSPF. I have read of course about performance issues and the risk of ...
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Hot potato routing topology

Im trying understand hot-potato routing better using this diagram that I have made. It shows R1 and R2 in automous system 1 (AS1) are receiving full routes from their parent providers P1 and P2 ...
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How to change the AS number without losing the old BGP configuration?

I use Cisco with IOSv and would like to change AS number without losing the old BGP configuration.How to change the AS number without losing the old BGP configuration?
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iBGP running only between BGP border routers?

I was studying about the BGP protocol and I had this question: Let's say we have an AS having both BGP border routers and internal routers . I know that the border routers should form a full mesh to ...
IlianaXn's user avatar
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Cisco ASA not accepting external traffic without NAT configuration

First of all, I am quite newie in the cisco world, so this could be some easy stuff that I'm missing. My first problem is trying to understand why a Cisco ASA5585 does not show traffic while doing a ...
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