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Is there no routing entry for loopback addresses?


How shall I understand the usage of the routing tables of a guest OS and its host OS?Routing 4 NetworksLinux routing table entry disappearsNetwork connectivity trouble to non-routing multi-homed hosts?Debian network disappearingrouting problem - arpBridge eth0 and wlan0How to create/setup vpn using only SSH?Internet connectivity using linux network namespaceNAT ETH1 PORT 5000 Traffic to PPP0Routing over Gateway













3















$ /sbin/route -n 
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.122.1 0.0.0.0 UG 0 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 ens3

$ /sbin/ifconfig
ens3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.202 netmask 255.255.255.0 broadcast 192.168.122.255
inet6 fe80::5054:ff:fe99:5eee prefixlen 64 scopeid 0x20<link>
ether 52:54:00:99:5e:ee txqueuelen 1000 (Ethernet)
RX packets 14906 bytes 18020195 (17.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 7390 bytes 786783 (768.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 35568

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 496 bytes 39840 (38.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 496 bytes 39840 (38.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


When a packet reaches the host and the packet is destined for the loop back address (127.0.0.1),



  • will it be transmitted to ens3 (192.168.122.202) and then to gateway (192.168.122.1), according to the first rule in the routing table?


  • If yes, isn't that wrong, since the intended destination (127.0.0.1) is in the local host?


Is there really no routing entry when destination addresses are loopback addresses?



Thanks.










share|improve this question
























  • Why you keep saying ent3? Shouldn't that be ens3 ?

    – 炸鱼薯条德里克
    yesterday






  • 1





    If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

    – Stephen Kitt
    yesterday















3















$ /sbin/route -n 
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.122.1 0.0.0.0 UG 0 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 ens3

$ /sbin/ifconfig
ens3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.202 netmask 255.255.255.0 broadcast 192.168.122.255
inet6 fe80::5054:ff:fe99:5eee prefixlen 64 scopeid 0x20<link>
ether 52:54:00:99:5e:ee txqueuelen 1000 (Ethernet)
RX packets 14906 bytes 18020195 (17.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 7390 bytes 786783 (768.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 35568

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 496 bytes 39840 (38.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 496 bytes 39840 (38.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


When a packet reaches the host and the packet is destined for the loop back address (127.0.0.1),



  • will it be transmitted to ens3 (192.168.122.202) and then to gateway (192.168.122.1), according to the first rule in the routing table?


  • If yes, isn't that wrong, since the intended destination (127.0.0.1) is in the local host?


Is there really no routing entry when destination addresses are loopback addresses?



Thanks.










share|improve this question
























  • Why you keep saying ent3? Shouldn't that be ens3 ?

    – 炸鱼薯条德里克
    yesterday






  • 1





    If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

    – Stephen Kitt
    yesterday













3












3








3








$ /sbin/route -n 
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.122.1 0.0.0.0 UG 0 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 ens3

$ /sbin/ifconfig
ens3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.202 netmask 255.255.255.0 broadcast 192.168.122.255
inet6 fe80::5054:ff:fe99:5eee prefixlen 64 scopeid 0x20<link>
ether 52:54:00:99:5e:ee txqueuelen 1000 (Ethernet)
RX packets 14906 bytes 18020195 (17.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 7390 bytes 786783 (768.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 35568

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 496 bytes 39840 (38.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 496 bytes 39840 (38.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


When a packet reaches the host and the packet is destined for the loop back address (127.0.0.1),



  • will it be transmitted to ens3 (192.168.122.202) and then to gateway (192.168.122.1), according to the first rule in the routing table?


  • If yes, isn't that wrong, since the intended destination (127.0.0.1) is in the local host?


Is there really no routing entry when destination addresses are loopback addresses?



Thanks.










share|improve this question
















$ /sbin/route -n 
Kernel IP routing table
Destination Gateway Genmask Flags Metric Ref Use Iface
0.0.0.0 192.168.122.1 0.0.0.0 UG 0 0 0 ens3
192.168.122.0 0.0.0.0 255.255.255.0 U 0 0 0 ens3

$ /sbin/ifconfig
ens3: flags=4163<UP,BROADCAST,RUNNING,MULTICAST> mtu 1500
inet 192.168.122.202 netmask 255.255.255.0 broadcast 192.168.122.255
inet6 fe80::5054:ff:fe99:5eee prefixlen 64 scopeid 0x20<link>
ether 52:54:00:99:5e:ee txqueuelen 1000 (Ethernet)
RX packets 14906 bytes 18020195 (17.1 MiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 7390 bytes 786783 (768.3 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 35568

lo: flags=73<UP,LOOPBACK,RUNNING> mtu 65536
inet 127.0.0.1 netmask 255.0.0.0
inet6 ::1 prefixlen 128 scopeid 0x10<host>
loop txqueuelen 1 (Local Loopback)
RX packets 496 bytes 39840 (38.9 KiB)
RX errors 0 dropped 0 overruns 0 frame 0
TX packets 496 bytes 39840 (38.9 KiB)
TX errors 0 dropped 0 overruns 0 carrier 0 collisions 0


When a packet reaches the host and the packet is destined for the loop back address (127.0.0.1),



  • will it be transmitted to ens3 (192.168.122.202) and then to gateway (192.168.122.1), according to the first rule in the routing table?


  • If yes, isn't that wrong, since the intended destination (127.0.0.1) is in the local host?


Is there really no routing entry when destination addresses are loopback addresses?



Thanks.







routing route






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited yesterday









Stephen Kitt

178k24405481




178k24405481










asked yesterday









TimTim

28.2k78269490




28.2k78269490












  • Why you keep saying ent3? Shouldn't that be ens3 ?

    – 炸鱼薯条德里克
    yesterday






  • 1





    If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

    – Stephen Kitt
    yesterday

















  • Why you keep saying ent3? Shouldn't that be ens3 ?

    – 炸鱼薯条德里克
    yesterday






  • 1





    If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

    – Stephen Kitt
    yesterday
















Why you keep saying ent3? Shouldn't that be ens3 ?

– 炸鱼薯条德里克
yesterday





Why you keep saying ent3? Shouldn't that be ens3 ?

– 炸鱼薯条德里克
yesterday




1




1





If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

– Stephen Kitt
yesterday





If you’re going to split your existing question into multiple questions, please delete the original first, it will avoid people wasting time writing answers to that one (as I have just done).

– Stephen Kitt
yesterday










1 Answer
1






active

oldest

votes


















6














The routing table isn’t the first thing taken into account when the kernel processes a packet; there’s a rule table which comes first, which you can see with ip rule list. ip route list (and the deprecated route) list the main table, but there’s a local table which has higher priority and lists all the routes involving the loopback interface; run ip route show table local to see them.



Packets addressed to a loopback address don’t leave the system.






share|improve this answer























  • Or ip -4 route show table all to show all the IPv4 entries

    – Stephen Harris
    yesterday











  • Can the deprecated route only access the routing table main, no the other two local and default?

    – Tim
    yesterday











  • I get the impression it can only access the main routing table, yes.

    – Stephen Kitt
    18 hours ago










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1 Answer
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active

oldest

votes








1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes









6














The routing table isn’t the first thing taken into account when the kernel processes a packet; there’s a rule table which comes first, which you can see with ip rule list. ip route list (and the deprecated route) list the main table, but there’s a local table which has higher priority and lists all the routes involving the loopback interface; run ip route show table local to see them.



Packets addressed to a loopback address don’t leave the system.






share|improve this answer























  • Or ip -4 route show table all to show all the IPv4 entries

    – Stephen Harris
    yesterday











  • Can the deprecated route only access the routing table main, no the other two local and default?

    – Tim
    yesterday











  • I get the impression it can only access the main routing table, yes.

    – Stephen Kitt
    18 hours ago















6














The routing table isn’t the first thing taken into account when the kernel processes a packet; there’s a rule table which comes first, which you can see with ip rule list. ip route list (and the deprecated route) list the main table, but there’s a local table which has higher priority and lists all the routes involving the loopback interface; run ip route show table local to see them.



Packets addressed to a loopback address don’t leave the system.






share|improve this answer























  • Or ip -4 route show table all to show all the IPv4 entries

    – Stephen Harris
    yesterday











  • Can the deprecated route only access the routing table main, no the other two local and default?

    – Tim
    yesterday











  • I get the impression it can only access the main routing table, yes.

    – Stephen Kitt
    18 hours ago













6












6








6







The routing table isn’t the first thing taken into account when the kernel processes a packet; there’s a rule table which comes first, which you can see with ip rule list. ip route list (and the deprecated route) list the main table, but there’s a local table which has higher priority and lists all the routes involving the loopback interface; run ip route show table local to see them.



Packets addressed to a loopback address don’t leave the system.






share|improve this answer













The routing table isn’t the first thing taken into account when the kernel processes a packet; there’s a rule table which comes first, which you can see with ip rule list. ip route list (and the deprecated route) list the main table, but there’s a local table which has higher priority and lists all the routes involving the loopback interface; run ip route show table local to see them.



Packets addressed to a loopback address don’t leave the system.







share|improve this answer












share|improve this answer



share|improve this answer










answered yesterday









Stephen KittStephen Kitt

178k24405481




178k24405481












  • Or ip -4 route show table all to show all the IPv4 entries

    – Stephen Harris
    yesterday











  • Can the deprecated route only access the routing table main, no the other two local and default?

    – Tim
    yesterday











  • I get the impression it can only access the main routing table, yes.

    – Stephen Kitt
    18 hours ago

















  • Or ip -4 route show table all to show all the IPv4 entries

    – Stephen Harris
    yesterday











  • Can the deprecated route only access the routing table main, no the other two local and default?

    – Tim
    yesterday











  • I get the impression it can only access the main routing table, yes.

    – Stephen Kitt
    18 hours ago
















Or ip -4 route show table all to show all the IPv4 entries

– Stephen Harris
yesterday





Or ip -4 route show table all to show all the IPv4 entries

– Stephen Harris
yesterday













Can the deprecated route only access the routing table main, no the other two local and default?

– Tim
yesterday





Can the deprecated route only access the routing table main, no the other two local and default?

– Tim
yesterday













I get the impression it can only access the main routing table, yes.

– Stephen Kitt
18 hours ago





I get the impression it can only access the main routing table, yes.

– Stephen Kitt
18 hours ago

















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