Questions tagged [prefix]

For questions about network prefixes, where the routing prefix may be expressed in Classless Inter-Domain Routing (CIDR) notation written as the first address of a network, followed by a slash character (/), and ending with the bit-length of the prefix. For instance, you are trying to find the prefix you want to announce on your router.

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Why can multiple ASNs have ROAs for the same prefix in RPKI?

I am trying to understand RPKI better and I am looking at some raw data dumps. My initial understanding of RPKI was that it would help identify and authenticate "the one" ASN that is ...
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2 answers
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Simple IPv6 Global Unicast question

I was reading this article which states: RFC 3587 states that out of the 128 bits in IPv6 addresses, left most three bits are must be fixed as 001. Remaining 45 bits are reserved for global routing ...
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6 votes
1 answer
649 views

IPv6 prefix interpretation

I have a very basic question about IPv6 prefix. Taking a very simple example about prefix notation: "2001:db8:abcd:0012::0/64" My question is: Do we call the whole thing under quote as ...
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1 answer
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How to choose IP address and subnet mask while forming a network

This question is bit novice. But, just wanted to clear any doubts as a starter for this topic. I have read about Classes of address like Class A, B, C. As I observe the Default Subnet mask for each of ...
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2 votes
1 answer
852 views

Prefix list BGP 0.0.0.0/0 and 0.0.0.0/ le 32

What is the difference between "ip prefix-list out seq 10 permit 0.0.0.0/0 and ip prefix-list out seq 10 permit 0.0.0.0/0 le 32?"
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3 votes
1 answer
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Recommended IPv6 prefix size for PPP to a single host?

I am using PPP to create a IPv6 connection to a remote host. What is the recommended IPv6 prefix size for a single host at the other end of the PPP connection? Should it be /128, because there is ...
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How do I determine an IP prefix? [duplicate]

I know barely nothing about computer networks. I am currently porting some windows code to linux, using .NET core. Some parts have not been implemented for linux, and determining an IP prefix is one ...
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BGP - Active\Passive Setup, except one AS

I have two transit providers, A and B. The business has chosen to make provider A more attractive due to billing concerns (we get attractive bulk pricing from this global provider). This was done by ...
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1 answer
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Find best route in route table using sorting [closed]

I am trying to implement a forwarding algorithm by myself with ARP, ICMP and the forwarding algorithms. Given the routing table: typedef struct route_table_entry { uint32_t prefix; uint32_t ...
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3 votes
2 answers
849 views

What determines the private ip addresses? [closed]

Right now, I am using internet at home, and my private ip address is 192.168.x.x. At work my private ip address is 10.x.x.x. In both of the scenarios, I did not play any role in selecting my ip, I ...
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3 votes
1 answer
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How to convert size represented in one prefix length to another?

Example, let's say if someone says, I have allocated one /64 address. How can I convert that to a size in /30? How many /30 equals to one /64?
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Subnetting different ip on same networks with different mask

I am a little confused with subnetting. Looking for a proper explanation. Suppose I have 3 routers A, B and C. Int 1: 10.0.0.1/30 <-- Router A Int 1: 10.0.0.2/30 <-- Router B Int 2: 10.0.0....
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5 votes
2 answers
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What does it mean to lease an IPv4 block?

When you lease an IPv4 block, what do you actually get? How do you get access to the IP addresses? Is there any special equipment required or is it as simple as renting a server?
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3 votes
1 answer
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Find which VRF contains a route

I am trying to find a Juniper command that shows a list of VRF routing tables that contain a specific prefix / range. Does any one know if this is possible? Thanks.
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2 votes
1 answer
738 views

Does IPv6 Prefix Delegation work with SLAAC, without the need of a DHCPv6 server/client?

All the (cisco) documentation I found about this topic always uses a DHCPv6 server or client to configure Prefix Delegation. But I never read that this is a requirement. Can Prefix Delegation be ...
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Does segment routing protocol steer packets based on best (longest) prefix matching?

In segment routing protocol, we know that the routing process is source steered. I'm struck to know if any best (longest) prefix matching happens to route the data packets? If so any clue about the ...
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1 vote
1 answer
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Find subnet prefix/CIDR from IP address and required No of hosts [duplicate]

I want to know that how can we calculate the Subnet prefix and CIDR, when the given information is only IP address and required No of hosts. For example: Suppose we have: IP Address= 198.1.1.0 and ...
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4 votes
3 answers
727 views

Problem with longest prefix matching

suppose we have two networks net1 = 192.24.0.0/18 and net2 = 192.24.12.0/22 and if we have a packet with destination IP as 192.24.12.8. So, according to longest prefix matching rule, we send this ...
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1 vote
1 answer
633 views

Question about BGP peering with your ISP

In you case you want to get rid of the static default route and you want to peer with your single ISP, do you need to announce any routes for your side ? I have the below config, is it enough for ...
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3 votes
1 answer
897 views

Bird BGP routing to iBGP router with prefix segmentation from /22 to four /24

First of all, I am a newbie to Bird and BGP routing. My question is, how can a router route traffic towards a lower router and segment from a one /22 prefix to four /24 prefixes? I tried to setup a ...
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1 vote
1 answer
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Automatically determining ipv6 prefix size to blacklist? [closed]

When writing blacklist automation for my network, is there a way to automatically determine the prefix size of the other party?
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14 votes
3 answers
2k views

Where can I use the IPv6 documentation prefix

We are currently building a networking course with a practical part where students have to configure a small network in a virtual environment. However, we are not sure what ipv6 prefixes we can use ...
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1 vote
1 answer
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IPv4 and IPv6 gateway subnet differences

I understand why for IPv4 the host and the gateway should be part of the same subnet, but for IPv6 I am a little bit confused. There are several types of IPv6 address assignment, but IPv6 requires the ...
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3 votes
1 answer
1k views

How to test an IP against a prefix list on JUNOS CLI

One can find routes matching an IP using show route 192.0.2.123. What is the equivalent way to find matching prefixes, if any, in a long prefix list? ... to determine quickly and conclusively whether ...
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14 votes
4 answers
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Possible (bit) patterns of a netmask

Given a prefix Y, it's easy to calculate the corresponding netmask: Put Y times a set bit, and then fill up "to the right" with zeros until one has 32 bits (IPv4) in total. Example: Prefix 24, thus ...
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1 vote
1 answer
137 views

Why is it impossible to advertise all OSPF /24 and not all /32 into BGP by using ACLs

For example: advertise all /24s from OSPF into BGP, but not the /32s. Impossible to do with access lists. the above statement can be found in this forum, in a question related to the differences ...
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4 votes
4 answers
761 views

Which ranges of IPv4 addresses cannot be expressed in prefix notation? [duplicate]

I was trying to do an exercise where we have a range of IPv4 addresses and we need to convert it both to "prefix notation", e.g. a.b.c.d/x, and to "address/mask". Now, apparently, the following ...
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2 votes
1 answer
336 views

Split prefix into several autonomous systems - BGP

Lets say I own (LIR-status) the prefix 80.200.72.0/21 and that prefix is routed via AS e.g. AS12345 at this very moment. Now I want to split this prefix into two AS, so the last portion (80.200.79.0/...
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2 votes
4 answers
116 views

Can I add a hop by dividing my prefix?

Let's say I have a /27 allocation from my ISP, and let's call it: 90.10.200.32/27 The ISP have their router set up as my gateway on address 90.10.200.33. The range 90.10.200.34-62 are free for me to ...
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3 votes
1 answer
837 views

Shorter prefix vs smaller prefix

Let's say we have network 1.0.0.0/16. Shorter prefixs than /16 are /0-/15. How about smaller prefix? The term "smaller prefix" is found in BGP-related documents.
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8 votes
2 answers
3k views

How is the IP prefix passed to the router?

First some background information on what I already know: An IPv4 address is a 32 bit address that identifies a node in a network. An IP address will have an IP prefix which determines the "Network" ...
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4 votes
1 answer
605 views

BGP routing based on ARIN info

I have discovered weird routing from our ISP all related to BGP. Here is the scenario (real-one). - there is a /19 prefix bought about 10 years ago, which was registered with ARIN authority. - as ...
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