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"Which entry of the routing table was selected?"
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Alex Vinokur
email: alex DOT vinokur AT gmail DOT com
http://mathforum.org/library/view/10978.html
http://sourceforge.net/users/alexvn
[
routing-table.txt ]
We consider only applications that have to call bind() to specify the source address of an outgoing connection.
Part 1. Settings
Table 1.1. Routing table
=========================================================================== ==========
Active Routes:
Network Destination Netmask Gateway Interface Metric Entry#
--------------------------------------------------------------------------- ----------
A B C D E
--------------------------------------------------------------------------- ----------
0.0.0.0 0.0.0.0 138.139.0.1 138.139.92.167 20 R1
10.1.1.0 255.255.255.0 10.1.1.125 10.1.1.125 20 R2
10.1.1.125 255.255.255.255 127.0.0.1 127.0.0.1 20 R3
10.255.255.255 255.255.255.255 10.1.1.125 10.1.1.125 20 R4
127.0.0.0 255.0.0.0 127.0.0.1 127.0.0.1 1 R5
138.139.0.0 255.255.0.0 138.139.92.167 138.139.92.167 20 R6
138.139.92.167 255.255.255.255 127.0.0.1 127.0.0.1 20 R7
138.139.255.255 255.255.255.255 138.139.92.167 138.139.92.167 20 R8
224.0.0.0 240.0.0.0 10.1.1.125 10.1.1.125 20 R9
224.0.0.0 240.0.0.0 138.139.92.167 138.139.92.167 20 R10
255.255.255.255 255.255.255.255 10.1.1.125 10.1.1.125 1 R11
255.255.255.255 255.255.255.255 138.139.92.167 138.139.92.167 1 R12
Default Gateway: 138.139.0.1
=========================================================================== ==========
Persistent Routes:
None
> ipconfig
Ethernet adapter Local Area Connection 2:
Connection-specific DNS Suffix . :
IP Address. . . . . . . . . . . . : 10.1.1.125
Subnet Mask . . . . . . . . . . . : 255.255.255.0
Default Gateway . . . . . . . . . :
Ethernet adapter Local Area Connection:
Connection-specific DNS Suffix . : <name>
IP Address. . . . . . . . . . . . : 138.139.92.167
Subnet Mask . . . . . . . . . . . : 255.255.0.0
Default Gateway . . . . . . . . . : 138.139.0.1
Part 2. Tests
Table 2.1. Messages sent and received using UDP sockets
=========================================================================== ==============
|| Receiver
Sender ||------------------------------------------------------------------------
|| 138.139.92.167 : 10.1.1.125 : 127.0.0.1 | 138.18.198.178 | 10.1.1.1
--------------------------------------------------------------------------- --------------
A || B : C : D | E | F
--------------------------------------------------------------------------- --------------
138.139.92.167 || Received : Received : Received | Received | Received
10.1.1.125 || Received : Received : Received | Received | Received
127.0.0.1 || Received : Received : Received | Not Received | Not Received
=========================================================================== ==============
Table 2.2. Routing for Table 2.1
=========================================================================== =======================================
| | Entries of routing table for the Receiver | Entry selected with longest prefix
| | per Interface according to | among Interfaces
| | (Netmask && ReceiverIP) == DestinationIP |------------------------------------
Sender | Receiver |-------------------------------------------| Interface equal to : Among
| | 138.139.92.167 : 10.1.1.125 : 127.0.0.1 | SourceIP : all Interfaces
--------------------------------------------------------------------------- ---------------------------------------
A | B | C : D : E | F : G
--------------------------------------------------------------------------- ---------------------------------------
138.139.92.167 | 138.139.92.167 | R6, R1 : : R7 | R6 (16 bits) : R7 (32 bits)
| 10.1.1.125 | R1 : R2 : R3 | R1 ( 0 bits) : R3 (32 bits)
| 127.0.0.1 | R1 : : R5 | R1 ( 0 bits) : R5 ( 8 bits)
| 138.18.198.178 | R1 : : | R1 ( 0 bits) : R1 ( 0 bits)
| 10.1.1.1 | R1 : R2 : | R1 ( 0 bits) : R2 (24 bits)
---------------|-----------------|----------------:------------:----------- --|------------------------------------
10.1.1.125 | 138.139.92.167 | R6, R1 : : R7 | - : R7 (32 bits)
| 10.1.1.125 | R1 : R2 : R3 | R2 (24 bits) : R3 (32 bits)
| 127.0.0.1 | R1 : : R5 | - : R5 ( 8 bits)
| 138.18.198.178 | R1 : : | - : R1 ( 0 bits)
| 10.1.1.1 | R1 : R2 : | R2 (24 bits) : R2 (24 bits)
---------------|-----------------|----------------:------------:----------- --|------------------------------------
127.0.0.1 | 138.139.92.167 | R6, R1 : : R7 | R7 (32 bits) : R7 (32 bits)
| 10.1.1.125 | R1 : R2 : R3 | R3 (32 bits) : R3 (32 bits)
| 127.0.0.1 | R1 : : R5 | R5 ( 8 bits) : R5 ( 8 bits)
=========================================================================== =======================================
Table 2.3. Question: What are routing table's entries selected for Table 2.1?
=========================================================================== ==============
|| Receiver
Sender ||------------------------------------------------------------------------
|| 138.139.92.167 : 10.1.1.125 : 127.0.0.1 | 138.18.198.178 | 10.1.1.1
--------------------------------------------------------------------------- --------------
A || B : C : D | E | F
--------------------------------------------------------------------------- --------------
138.139.92.167 || R7 or R6? : R3 or R1? : R5 or R1? | R1 | R2 or R1?
10.1.1.125 || R7? : R3 or R2? : R5? | R1? | R2
127.0.0.1 || R7 : R3 : R5 | - | -
=========================================================================== ==============
P.S. It seems that the "Interface" column of routing table doesn't matter (for applications calling bind()
to specify the source address of an outgoing connection)? Is it truth?
