Kernel Routing Table - Interface specific routes
I have a question on kernel routing table. It will be great if any of you can throw some light on this topic
In general, whenever an inteface is brought to 'up' state, an interface route comes up. for ex. If eth0 with Ip address 192.168.10.0 is brought up, the following route is created by default
"192.168.10.0 0.0.0.0 255.255.255.0 U 0 0 0 eth0"
After this route is created, if i try to add the same route manually, with the following command, the same route gets added again.
"route add -net 192.168.10.0 netmask 255.255.255.0 dev eth0"
I do not see any difference in both of these routes when i verified with 'route -n' or 'netstat -r' or 'cat /proc/net/route'. How is this possible?
In general, at any point of time, you cannot have two same entries in the kernel routing table. Can any of the linux expert help me with this question??
Regards,
Joe
Comments
-
with route you can and should add gateway.0
-
In the case of network specifc routes, gateway address will be 0.0.0.0. try route -n on any linux Box/PC and verify.
My question is how can there be two identical routes in the routing table at a point of time.
-Joe0 -
== newbiesh
0.0.0.0 is your IP of the interface. if your IP is 192.168.1.100, then 0.0.0.0 is equal to this. 0.0.0.0 is something like localhost, but uses the ethX interface and its IP.
this is my route -nKernel IP routing table Destination Gateway Genmask Flags Metric Ref Use Iface 192.168.1.0 0.0.0.0 255.255.255.0 U 202 0 0 eth0 0.0.0.0 192.168.1.1 0.0.0.0 UG 202 0 0 eth0
as you see they are not identical. the first line is for incoming trafic and the second for the outgoing (or vice versa).
in my case to add gateway i should use:route add -host 192.168.1.1
i hope you know the diffrence betwen -host and -net.
== end-newbiesh (LoL)
So maybe is wrong with the init script. but be sure that if you still have net then everythink is okey. it does not matter wich one of the 2 equal lines the kernel is using, becaouse they are pointing at same thing. the solution is to write a patch wich makes (unnesessery) checking for existance of the route before adding it.
so dont worry about it. i hope i've helped you in some or other way.0 -
The situation which you have explained is the difference between default route (route to 0.0.0.0 destination) and the interface specifc route (destination 192.168.1.0).
My question is different. Probably, i did not explain it clearly enough. Let me try to explain the situation with an example.
Consider the scenario where you have eth1 interface with IP address as 192.168.1.1. In such a case when the interface comes up (assuming that there is no other route configured) , the following is the entry in the kernel route table
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
Now, if i try to add the same entry again into the kernel routing table using the following command, the entry gets added and route entry shows two similar entries
route add -net 192.168.1.0 dev eth1
Destination Gateway Genmask Flags Metric Ref Use Iface
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
192.168.1.0 0.0.0.0 255.255.255.0 U 0 0 0 eth1
I understand that there will not be any problem because of this duplicate rule. But, Can someone clarify the following questions based on the scenario which i explained above?
1. Are these two entries (the entry which got added by default and the entry which i added manually) different by any means??
2. why should there be two similar routes in the kernel routing table?
3. Is there a patch available to solve this?
4. In general, there should not be identical entries in the kernel routing table. 5. Is this not applicable to all routing entries (be it host specific, default route or interface specific route)?
Regards
Joe0
Categories
- All Categories
- 51 LFX Mentorship
- 104 LFX Mentorship: Linux Kernel
- 576 Linux Foundation IT Professional Programs
- 304 Cloud Engineer IT Professional Program
- 125 Advanced Cloud Engineer IT Professional Program
- 53 DevOps Engineer IT Professional Program
- 61 Cloud Native Developer IT Professional Program
- 5 Express Training Courses
- 5 Express Courses - Discussion Forum
- 2K Training Courses
- 19 LFC110 Class Forum
- 7 LFC131 Class Forum
- 27 LFD102 Class Forum
- 157 LFD103 Class Forum
- 20 LFD121 Class Forum
- 1 LFD137 Class Forum
- 61 LFD201 Class Forum
- 1 LFD210 Class Forum
- LFD210-CN Class Forum
- 1 LFD213 Class Forum - Discontinued
- 128 LFD232 Class Forum
- LFD237 Class Forum
- 23 LFD254 Class Forum
- 611 LFD259 Class Forum
- 105 LFD272 Class Forum
- 1 LFD272-JP クラス フォーラム
- 1 LFD273 Class Forum
- 2 LFS145 Class Forum
- 24 LFS200 Class Forum
- 739 LFS201 Class Forum
- 1 LFS201-JP クラス フォーラム
- 11 LFS203 Class Forum
- 75 LFS207 Class Forum
- 300 LFS211 Class Forum
- 54 LFS216 Class Forum
- 47 LFS241 Class Forum
- 41 LFS242 Class Forum
- 37 LFS243 Class Forum
- 11 LFS244 Class Forum
- 36 LFS250 Class Forum
- 1 LFS250-JP クラス フォーラム
- LFS251 Class Forum
- 140 LFS253 Class Forum
- LFS254 Class Forum
- 1.1K LFS258 Class Forum
- 10 LFS258-JP クラス フォーラム
- 93 LFS260 Class Forum
- 132 LFS261 Class Forum
- 33 LFS262 Class Forum
- 80 LFS263 Class Forum
- 15 LFS264 Class Forum
- 11 LFS266 Class Forum
- 18 LFS267 Class Forum
- 17 LFS268 Class Forum
- 23 LFS269 Class Forum
- 203 LFS272 Class Forum
- 1 LFS272-JP クラス フォーラム
- LFS274 Class Forum
- LFS281 Class Forum
- 235 LFW211 Class Forum
- 172 LFW212 Class Forum
- 7 SKF100 Class Forum
- SKF200 Class Forum
- 903 Hardware
- 219 Drivers
- 74 I/O Devices
- 44 Monitors
- 116 Multimedia
- 209 Networking
- 101 Printers & Scanners
- 85 Storage
- 763 Linux Distributions
- 88 Debian
- 66 Fedora
- 15 Linux Mint
- 13 Mageia
- 24 openSUSE
- 142 Red Hat Enterprise
- 33 Slackware
- 13 SUSE Enterprise
- 357 Ubuntu
- 479 Linux System Administration
- 41 Cloud Computing
- 70 Command Line/Scripting
- Github systems admin projects
- 95 Linux Security
- 78 Network Management
- 108 System Management
- 49 Web Management
- 68 Mobile Computing
- 23 Android
- 30 Development
- 1.2K New to Linux
- 1.1K Getting Started with Linux
- 537 Off Topic
- 131 Introductions
- 217 Small Talk
- 21 Study Material
- 826 Programming and Development
- 278 Kernel Development
- 514 Software Development
- 928 Software
- 260 Applications
- 184 Command Line
- 3 Compiling/Installing
- 76 Games
- 316 Installation
- 61 All In Program
- 61 All In Forum
Upcoming Training
-
August 20, 2018
Kubernetes Administration (LFS458)
-
August 20, 2018
Linux System Administration (LFS301)
-
August 27, 2018
Open Source Virtualization (LFS462)
-
August 27, 2018
Linux Kernel Debugging and Security (LFD440)