What is the interface scope (global vs. link) used for?
up vote
8
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Routing table entries have an attribute scope. I would like to know how the change from global to link (or the other way round) affects the network system.
linux networking routing
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
add a comment |
up vote
8
down vote
favorite
Routing table entries have an attribute scope. I would like to know how the change from global to link (or the other way round) affects the network system.
linux networking routing
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
I can't chek but in the man ip(8) there's the valuescope SCOPE_VALUEthat can be global, link, site, host but it seems related to address and not route
– Kiwy
Apr 4 '14 at 8:12
add a comment |
up vote
8
down vote
favorite
up vote
8
down vote
favorite
Routing table entries have an attribute scope. I would like to know how the change from global to link (or the other way round) affects the network system.
linux networking routing
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
Routing table entries have an attribute scope. I would like to know how the change from global to link (or the other way round) affects the network system.
linux networking routing
linux networking routing
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
asked Apr 4 '14 at 7:36
Hauke Laging
55.6k1285133
55.6k1285133
I can't chek but in the man ip(8) there's the valuescope SCOPE_VALUEthat can be global, link, site, host but it seems related to address and not route
– Kiwy
Apr 4 '14 at 8:12
add a comment |
I can't chek but in the man ip(8) there's the valuescope SCOPE_VALUEthat can be global, link, site, host but it seems related to address and not route
– Kiwy
Apr 4 '14 at 8:12
I can't chek but in the man ip(8) there's the value
scope SCOPE_VALUE that can be global, link, site, host but it seems related to address and not route– Kiwy
Apr 4 '14 at 8:12
I can't chek but in the man ip(8) there's the value
scope SCOPE_VALUE that can be global, link, site, host but it seems related to address and not route– Kiwy
Apr 4 '14 at 8:12
add a comment |
2 Answers
2
active
oldest
votes
up vote
4
down vote
Let look at route scope definition in Linux:
The scope of a route in Linux is an indicator of the distance to the
destination network.
Host
A route has host scope when it leads to a destination address on the local host.
Link
A route has link scope when it leads to a destination address on the local network.
Universe
A route has universe scope when it leads to addresses more than one hop away.
So if you change the scope of a route, your computer probably can not connect to network in that route anymore. The router simply doesn't forward the packet which is send to destination belongs local network.
Note that the scope does not reflect the distinction between nonroutable (private) and routable (public) addresses.
Both 10.0.0.1 (private - non routeable) and 8.8.8.8 (public - routable) can be given either link or universe (global) scope. It is configured by system administrator.
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
add a comment |
up vote
2
down vote
The scope influences source address selection.
For connections/associations where the source address is not yet fixed (e.g. initiating a TCP connection, but not when reacting to an incoming packet), the source address will be selected depending on the scope of the route the packet is about to hit.
This is why addresses also have a scope attribute.
Example where no source address selection occurs: an incoming TCP connection initiation or ping packet will be answered with the IP addresses reversed (source → destination, destination → source), otherwise the other host would not recognize the packet as answer.
Example where source address selection occurs: ping xyz or telnet xyz. Common programs do not tell the operating system which source address to use (and that is a good habit). The OS needs to pick one and is prepared to do so: it tests the potential outgoing packet for the route it would hit (normal routing uses the destination address only, if you use advanced routing, the packet will not have a source address yet!). The resulting scope reduces the selection to addresses from the corresponding scope on the outgoing interface if any are available.
answered May 11 '16 at 18:13
Robert Siemer
640718
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
add a comment |
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2 Answers
2
active
oldest
votes
2 Answers
2
active
oldest
votes
active
oldest
votes
active
oldest
votes
up vote
4
down vote
Let look at route scope definition in Linux:
The scope of a route in Linux is an indicator of the distance to the
destination network.
Host
A route has host scope when it leads to a destination address on the local host.
Link
A route has link scope when it leads to a destination address on the local network.
Universe
A route has universe scope when it leads to addresses more than one hop away.
So if you change the scope of a route, your computer probably can not connect to network in that route anymore. The router simply doesn't forward the packet which is send to destination belongs local network.
Note that the scope does not reflect the distinction between nonroutable (private) and routable (public) addresses.
Both 10.0.0.1 (private - non routeable) and 8.8.8.8 (public - routable) can be given either link or universe (global) scope. It is configured by system administrator.
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
add a comment |
up vote
4
down vote
Let look at route scope definition in Linux:
The scope of a route in Linux is an indicator of the distance to the
destination network.
Host
A route has host scope when it leads to a destination address on the local host.
Link
A route has link scope when it leads to a destination address on the local network.
Universe
A route has universe scope when it leads to addresses more than one hop away.
So if you change the scope of a route, your computer probably can not connect to network in that route anymore. The router simply doesn't forward the packet which is send to destination belongs local network.
Note that the scope does not reflect the distinction between nonroutable (private) and routable (public) addresses.
Both 10.0.0.1 (private - non routeable) and 8.8.8.8 (public - routable) can be given either link or universe (global) scope. It is configured by system administrator.
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
add a comment |
up vote
4
down vote
up vote
4
down vote
Let look at route scope definition in Linux:
The scope of a route in Linux is an indicator of the distance to the
destination network.
Host
A route has host scope when it leads to a destination address on the local host.
Link
A route has link scope when it leads to a destination address on the local network.
Universe
A route has universe scope when it leads to addresses more than one hop away.
So if you change the scope of a route, your computer probably can not connect to network in that route anymore. The router simply doesn't forward the packet which is send to destination belongs local network.
Note that the scope does not reflect the distinction between nonroutable (private) and routable (public) addresses.
Both 10.0.0.1 (private - non routeable) and 8.8.8.8 (public - routable) can be given either link or universe (global) scope. It is configured by system administrator.
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
Let look at route scope definition in Linux:
The scope of a route in Linux is an indicator of the distance to the
destination network.
Host
A route has host scope when it leads to a destination address on the local host.
Link
A route has link scope when it leads to a destination address on the local network.
Universe
A route has universe scope when it leads to addresses more than one hop away.
So if you change the scope of a route, your computer probably can not connect to network in that route anymore. The router simply doesn't forward the packet which is send to destination belongs local network.
Note that the scope does not reflect the distinction between nonroutable (private) and routable (public) addresses.
Both 10.0.0.1 (private - non routeable) and 8.8.8.8 (public - routable) can be given either link or universe (global) scope. It is configured by system administrator.
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
edited Apr 4 '14 at 10:03
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
answered Apr 4 '14 at 9:51
cuonglm
102k23198299
102k23198299
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
add a comment |
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
So ... nothing to do with the BGP scope, aka route scoping for high-level routing protocols (sigh)
– Ouki
Apr 4 '14 at 12:09
1
1
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
Small nitpicking here: in IPv4, all addresses are routable, including 10.0.0.0/8 and 192.168.0.0/16 -- but 10.0.0.0/8 isn't routed in public networks. But you can still route them, for instance, inside your subnetted 10.0.0.0/8. Only with IPv6 there are unroutable addresses, namely ::1 and LLAs.
– TheDiveO
Apr 26 at 10:56
add a comment |
up vote
2
down vote
The scope influences source address selection.
For connections/associations where the source address is not yet fixed (e.g. initiating a TCP connection, but not when reacting to an incoming packet), the source address will be selected depending on the scope of the route the packet is about to hit.
This is why addresses also have a scope attribute.
Example where no source address selection occurs: an incoming TCP connection initiation or ping packet will be answered with the IP addresses reversed (source → destination, destination → source), otherwise the other host would not recognize the packet as answer.
Example where source address selection occurs: ping xyz or telnet xyz. Common programs do not tell the operating system which source address to use (and that is a good habit). The OS needs to pick one and is prepared to do so: it tests the potential outgoing packet for the route it would hit (normal routing uses the destination address only, if you use advanced routing, the packet will not have a source address yet!). The resulting scope reduces the selection to addresses from the corresponding scope on the outgoing interface if any are available.
answered May 11 '16 at 18:13
Robert Siemer
640718
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
add a comment |
up vote
2
down vote
The scope influences source address selection.
For connections/associations where the source address is not yet fixed (e.g. initiating a TCP connection, but not when reacting to an incoming packet), the source address will be selected depending on the scope of the route the packet is about to hit.
This is why addresses also have a scope attribute.
Example where no source address selection occurs: an incoming TCP connection initiation or ping packet will be answered with the IP addresses reversed (source → destination, destination → source), otherwise the other host would not recognize the packet as answer.
Example where source address selection occurs: ping xyz or telnet xyz. Common programs do not tell the operating system which source address to use (and that is a good habit). The OS needs to pick one and is prepared to do so: it tests the potential outgoing packet for the route it would hit (normal routing uses the destination address only, if you use advanced routing, the packet will not have a source address yet!). The resulting scope reduces the selection to addresses from the corresponding scope on the outgoing interface if any are available.
answered May 11 '16 at 18:13
Robert Siemer
640718
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
add a comment |
up vote
2
down vote
up vote
2
down vote
The scope influences source address selection.
For connections/associations where the source address is not yet fixed (e.g. initiating a TCP connection, but not when reacting to an incoming packet), the source address will be selected depending on the scope of the route the packet is about to hit.
This is why addresses also have a scope attribute.
Example where no source address selection occurs: an incoming TCP connection initiation or ping packet will be answered with the IP addresses reversed (source → destination, destination → source), otherwise the other host would not recognize the packet as answer.
Example where source address selection occurs: ping xyz or telnet xyz. Common programs do not tell the operating system which source address to use (and that is a good habit). The OS needs to pick one and is prepared to do so: it tests the potential outgoing packet for the route it would hit (normal routing uses the destination address only, if you use advanced routing, the packet will not have a source address yet!). The resulting scope reduces the selection to addresses from the corresponding scope on the outgoing interface if any are available.
answered May 11 '16 at 18:13
Robert Siemer
640718
The scope influences source address selection.
For connections/associations where the source address is not yet fixed (e.g. initiating a TCP connection, but not when reacting to an incoming packet), the source address will be selected depending on the scope of the route the packet is about to hit.
This is why addresses also have a scope attribute.
Example where no source address selection occurs: an incoming TCP connection initiation or ping packet will be answered with the IP addresses reversed (source → destination, destination → source), otherwise the other host would not recognize the packet as answer.
Example where source address selection occurs: ping xyz or telnet xyz. Common programs do not tell the operating system which source address to use (and that is a good habit). The OS needs to pick one and is prepared to do so: it tests the potential outgoing packet for the route it would hit (normal routing uses the destination address only, if you use advanced routing, the packet will not have a source address yet!). The resulting scope reduces the selection to addresses from the corresponding scope on the outgoing interface if any are available.
answered May 11 '16 at 18:13
Robert Siemer
640718
edited 2 days ago
answered May 11 '16 at 18:13
Robert Siemer
640718
answered May 11 '16 at 18:13
Robert Siemer
640718
answered May 11 '16 at 18:13
Robert Siemer
640718
640718
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
add a comment |
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
Do you have a literature reference for your statement "scope influences address selection" that explicitly links this to routes? My understanding of RFC 6724 is that only addresses have scope, but the RFC is silent on any scope property of routes. If there is in fact a scope defined for routes, it would be great if you could reference it in your answer. Thanks!
– TheDiveO
Apr 26 at 10:53
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
@TheDiveO That fact is already part of the question I'm answering here.
– Robert Siemer
Apr 26 at 22:26
add a comment |
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I can't chek but in the man ip(8) there's the value
scope SCOPE_VALUEthat can be global, link, site, host but it seems related to address and not route– Kiwy
Apr 4 '14 at 8:12