Can I announce prefix 161.117.25.0/24 even though I don't have all of /24 IPs?Basic network setup for...
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Can I announce prefix 161.117.25.0/24 even though I don't have all of /24 IPs?
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Can I announce prefix 161.117.25.0/24 even though I don't have all of /24 IPs?
Basic network setup for colocation / several cabinets and related questionsSetup the BGP + ospf networkWhen is BGP needed?BGP loadbalancing: full bgp table vs default route onlyBGP - how does IGP know the right route?BGP - use prefix on 2 locationsPreferred anycast paths for DNS with Quagga BGPProblem with ibgp configurationDefining hierarchical BGP route-mapsQuagga - Configure 3 routers using OSPF
I'm managing one BGP router, under the router I'm trying to announce the following IP prefix:161.117.25.0/24. But the problem is that some of the IP addresses were borrowed by other AS(Autonomous System), for example the IP address 161.117.25.100 and 161.117.25.200 were borrowed by other AS. So how should I announce the remaining IP addresses please.
Following questions please:
- Can I announce
161.117.25.0/30? - Is it possible that two Autonomous Systems announce or have the same IP prefix?
router bgp
edited 7 hours ago
Community♦
1
asked 18 hours ago
JackJack
1716
add a comment |
I'm managing one BGP router, under the router I'm trying to announce the following IP prefix:161.117.25.0/24. But the problem is that some of the IP addresses were borrowed by other AS(Autonomous System), for example the IP address 161.117.25.100 and 161.117.25.200 were borrowed by other AS. So how should I announce the remaining IP addresses please.
Following questions please:
- Can I announce
161.117.25.0/30? - Is it possible that two Autonomous Systems announce or have the same IP prefix?
router bgp
edited 7 hours ago
Community♦
1
asked 18 hours ago
JackJack
1716
1
ISPs will only advertise/24or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.
– Ron Maupin♦
16 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago
add a comment |
I'm managing one BGP router, under the router I'm trying to announce the following IP prefix:161.117.25.0/24. But the problem is that some of the IP addresses were borrowed by other AS(Autonomous System), for example the IP address 161.117.25.100 and 161.117.25.200 were borrowed by other AS. So how should I announce the remaining IP addresses please.
Following questions please:
- Can I announce
161.117.25.0/30? - Is it possible that two Autonomous Systems announce or have the same IP prefix?
router bgp
edited 7 hours ago
Community♦
1
asked 18 hours ago
JackJack
1716
I'm managing one BGP router, under the router I'm trying to announce the following IP prefix:161.117.25.0/24. But the problem is that some of the IP addresses were borrowed by other AS(Autonomous System), for example the IP address 161.117.25.100 and 161.117.25.200 were borrowed by other AS. So how should I announce the remaining IP addresses please.
Following questions please:
- Can I announce
161.117.25.0/30? - Is it possible that two Autonomous Systems announce or have the same IP prefix?
router bgp
router bgp
edited 7 hours ago
Community♦
1
asked 18 hours ago
JackJack
1716
edited 7 hours ago
Community♦
1
asked 18 hours ago
JackJack
1716
edited 7 hours ago
Community♦
1
edited 7 hours ago
Community♦
1
edited 7 hours ago
Community♦
1
1
asked 18 hours ago
JackJack
1716
asked 18 hours ago
JackJack
1716
asked 18 hours ago
JackJack
1716
1716
1
ISPs will only advertise/24or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.
– Ron Maupin♦
16 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago
add a comment |
1
ISPs will only advertise/24or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.
– Ron Maupin♦
16 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago
1
1
ISPs will only advertise
/24 or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.– Ron Maupin♦
16 hours ago
ISPs will only advertise
/24 or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.– Ron Maupin♦
16 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago
add a comment |
3 Answers
3
active
oldest
votes
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 been assigned a number of IP addresses to use from that /24. However, that does not give you the right to advertise them under your own ASN in BGP. If you do so, it would be considered a BGP Hijack.
Hopefully, it wouldn't work very well due to filters in place at upstream networks, but if it would, IP addresses in that /24 used by others would become unreachable.
The conclusion here is: you don't announce the /24 unless you're authorized to do so.
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
add a comment |
Is it possible that two Autonomous Systems announce or have the same ip prefix?
It is entirely possible for multiple ASNs to announce the same prefix -- the shortest AS-PATH from any given perspective "wins". However, it's a poor practice that will trigger warnings in any BGP monitoring systems. (see also: route hijacking) If AS1 and AS2 both announce the same prefix, those closest to AS1 will prefer AS1; those closest to AS2 will prefer AS2. As long as you are connected to both ASNs it will usually work, but you've create a very fragile arrangement.
Beyond BGP (once routes are in the FIB), IP routing uses a longest-match algorithm. The /32 routes for 100 and 200 will match before the /24 (which will match before the /16, etc.) As others have already said, one cannot announce [BGP] anything more specific than /24 globally, so it would be up to you and/or your ISP(s) to make sure those two specific addresses are handled appropriately.
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
add a comment |
Just to be concrete, you advertise the blocks you do have. Given a "/24 without .100 and .200", the minimal number of blocks is 14:
A.B.C.0/26
A.B.C.64/27
A.B.C.96/30
A.B.C.101/32
A.B.C.102/31
A.B.C.104/29
A.B.C.112/28
A.B.C.128/26
A.B.C.192/29
A.B.C.201/32
A.B.C.202/31
A.B.C.204/30
A.B.C.208/28
A.B.C.224/27
Whether your ISP or other organisation will accept such long prefixes is a matter to take up with them: most ISPs have a limit shorter than /24/
Other, non-minimal, groupings are also possible in principle, up to the limiting case of 254 blocks each /32.
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
add a comment |
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3 Answers
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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 been assigned a number of IP addresses to use from that /24. However, that does not give you the right to advertise them under your own ASN in BGP. If you do so, it would be considered a BGP Hijack.
Hopefully, it wouldn't work very well due to filters in place at upstream networks, but if it would, IP addresses in that /24 used by others would become unreachable.
The conclusion here is: you don't announce the /24 unless you're authorized to do so.
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
add a comment |
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 been assigned a number of IP addresses to use from that /24. However, that does not give you the right to advertise them under your own ASN in BGP. If you do so, it would be considered a BGP Hijack.
Hopefully, it wouldn't work very well due to filters in place at upstream networks, but if it would, IP addresses in that /24 used by others would become unreachable.
The conclusion here is: you don't announce the /24 unless you're authorized to do so.
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
add a comment |
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 been assigned a number of IP addresses to use from that /24. However, that does not give you the right to advertise them under your own ASN in BGP. If you do so, it would be considered a BGP Hijack.
Hopefully, it wouldn't work very well due to filters in place at upstream networks, but if it would, IP addresses in that /24 used by others would become unreachable.
The conclusion here is: you don't announce the /24 unless you're authorized to do so.
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
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 been assigned a number of IP addresses to use from that /24. However, that does not give you the right to advertise them under your own ASN in BGP. If you do so, it would be considered a BGP Hijack.
Hopefully, it wouldn't work very well due to filters in place at upstream networks, but if it would, IP addresses in that /24 used by others would become unreachable.
The conclusion here is: you don't announce the /24 unless you're authorized to do so.
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
answered 18 hours ago
Teun Vink♦Teun Vink
11.7k53154
11.7k53154
add a comment |
add a comment |
Is it possible that two Autonomous Systems announce or have the same ip prefix?
It is entirely possible for multiple ASNs to announce the same prefix -- the shortest AS-PATH from any given perspective "wins". However, it's a poor practice that will trigger warnings in any BGP monitoring systems. (see also: route hijacking) If AS1 and AS2 both announce the same prefix, those closest to AS1 will prefer AS1; those closest to AS2 will prefer AS2. As long as you are connected to both ASNs it will usually work, but you've create a very fragile arrangement.
Beyond BGP (once routes are in the FIB), IP routing uses a longest-match algorithm. The /32 routes for 100 and 200 will match before the /24 (which will match before the /16, etc.) As others have already said, one cannot announce [BGP] anything more specific than /24 globally, so it would be up to you and/or your ISP(s) to make sure those two specific addresses are handled appropriately.
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
add a comment |
Is it possible that two Autonomous Systems announce or have the same ip prefix?
It is entirely possible for multiple ASNs to announce the same prefix -- the shortest AS-PATH from any given perspective "wins". However, it's a poor practice that will trigger warnings in any BGP monitoring systems. (see also: route hijacking) If AS1 and AS2 both announce the same prefix, those closest to AS1 will prefer AS1; those closest to AS2 will prefer AS2. As long as you are connected to both ASNs it will usually work, but you've create a very fragile arrangement.
Beyond BGP (once routes are in the FIB), IP routing uses a longest-match algorithm. The /32 routes for 100 and 200 will match before the /24 (which will match before the /16, etc.) As others have already said, one cannot announce [BGP] anything more specific than /24 globally, so it would be up to you and/or your ISP(s) to make sure those two specific addresses are handled appropriately.
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
add a comment |
Is it possible that two Autonomous Systems announce or have the same ip prefix?
It is entirely possible for multiple ASNs to announce the same prefix -- the shortest AS-PATH from any given perspective "wins". However, it's a poor practice that will trigger warnings in any BGP monitoring systems. (see also: route hijacking) If AS1 and AS2 both announce the same prefix, those closest to AS1 will prefer AS1; those closest to AS2 will prefer AS2. As long as you are connected to both ASNs it will usually work, but you've create a very fragile arrangement.
Beyond BGP (once routes are in the FIB), IP routing uses a longest-match algorithm. The /32 routes for 100 and 200 will match before the /24 (which will match before the /16, etc.) As others have already said, one cannot announce [BGP] anything more specific than /24 globally, so it would be up to you and/or your ISP(s) to make sure those two specific addresses are handled appropriately.
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
Is it possible that two Autonomous Systems announce or have the same ip prefix?
It is entirely possible for multiple ASNs to announce the same prefix -- the shortest AS-PATH from any given perspective "wins". However, it's a poor practice that will trigger warnings in any BGP monitoring systems. (see also: route hijacking) If AS1 and AS2 both announce the same prefix, those closest to AS1 will prefer AS1; those closest to AS2 will prefer AS2. As long as you are connected to both ASNs it will usually work, but you've create a very fragile arrangement.
Beyond BGP (once routes are in the FIB), IP routing uses a longest-match algorithm. The /32 routes for 100 and 200 will match before the /24 (which will match before the /16, etc.) As others have already said, one cannot announce [BGP] anything more specific than /24 globally, so it would be up to you and/or your ISP(s) to make sure those two specific addresses are handled appropriately.
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
answered 13 hours ago
Ricky BeamRicky Beam
21.9k22961
21.9k22961
add a comment |
add a comment |
Just to be concrete, you advertise the blocks you do have. Given a "/24 without .100 and .200", the minimal number of blocks is 14:
A.B.C.0/26
A.B.C.64/27
A.B.C.96/30
A.B.C.101/32
A.B.C.102/31
A.B.C.104/29
A.B.C.112/28
A.B.C.128/26
A.B.C.192/29
A.B.C.201/32
A.B.C.202/31
A.B.C.204/30
A.B.C.208/28
A.B.C.224/27
Whether your ISP or other organisation will accept such long prefixes is a matter to take up with them: most ISPs have a limit shorter than /24/
Other, non-minimal, groupings are also possible in principle, up to the limiting case of 254 blocks each /32.
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
add a comment |
Just to be concrete, you advertise the blocks you do have. Given a "/24 without .100 and .200", the minimal number of blocks is 14:
A.B.C.0/26
A.B.C.64/27
A.B.C.96/30
A.B.C.101/32
A.B.C.102/31
A.B.C.104/29
A.B.C.112/28
A.B.C.128/26
A.B.C.192/29
A.B.C.201/32
A.B.C.202/31
A.B.C.204/30
A.B.C.208/28
A.B.C.224/27
Whether your ISP or other organisation will accept such long prefixes is a matter to take up with them: most ISPs have a limit shorter than /24/
Other, non-minimal, groupings are also possible in principle, up to the limiting case of 254 blocks each /32.
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
add a comment |
Just to be concrete, you advertise the blocks you do have. Given a "/24 without .100 and .200", the minimal number of blocks is 14:
A.B.C.0/26
A.B.C.64/27
A.B.C.96/30
A.B.C.101/32
A.B.C.102/31
A.B.C.104/29
A.B.C.112/28
A.B.C.128/26
A.B.C.192/29
A.B.C.201/32
A.B.C.202/31
A.B.C.204/30
A.B.C.208/28
A.B.C.224/27
Whether your ISP or other organisation will accept such long prefixes is a matter to take up with them: most ISPs have a limit shorter than /24/
Other, non-minimal, groupings are also possible in principle, up to the limiting case of 254 blocks each /32.
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
Just to be concrete, you advertise the blocks you do have. Given a "/24 without .100 and .200", the minimal number of blocks is 14:
A.B.C.0/26
A.B.C.64/27
A.B.C.96/30
A.B.C.101/32
A.B.C.102/31
A.B.C.104/29
A.B.C.112/28
A.B.C.128/26
A.B.C.192/29
A.B.C.201/32
A.B.C.202/31
A.B.C.204/30
A.B.C.208/28
A.B.C.224/27
Whether your ISP or other organisation will accept such long prefixes is a matter to take up with them: most ISPs have a limit shorter than /24/
Other, non-minimal, groupings are also possible in principle, up to the limiting case of 254 blocks each /32.
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
edited 15 hours ago
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
answered 15 hours ago
jonathanjojonathanjo
11.7k1935
11.7k1935
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
add a comment |
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
If 161.117.25.0/24 is assigned to a LAN, some trickery would be necessary to put 100 and 200 somewhere else. (I've done this very thing.) From a route table perspective, 161.117.25.0/24, 161.117.25.100/32, 161.117.25.200/32 do not create a conflict.
– Ricky Beam
13 hours ago
add a comment |
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1
ISPs will only advertise
/24or shorter IPv4 prefixes. You need to ask your ISP if you can announce a longer prefix to it, but it will not advertise it to the Internet. No, two ASes advertising the same prefix will break things, and likely get both blocked.– Ron Maupin♦
16 hours ago
Is the prefix yours or not? It does not appear to be publicly assigned to you. It should go without saying that if the prefix is not yours, you can't announce it.
– David Schwartz
13 hours ago