ji_setup.txt

网上下到的一个很详细介绍VPN基础知识的资料

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* RCSID $Id: ji_setup.txt,v 1.6 1999/04/06 04:54:23 rgb Exp $
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[Here is JI's setup.  This document is OBSOLETE (rgb, May 6, 1998) but is
included for historical purposes and the concepts are still relevant
although commands and syntax have changed significantly.

Here is a simplified view of JI's testbed:


    +-------+						    +-------+
    |  elf  |						    |  del  |
    +---*---+						    +---*---+
   eth1 * 10.1.0.145      	        		    ef1 * 10.3.0.140
	*							*
    *************************               *************************
			*			*
                   eth1 * 10.1.0.143       eth2 * 10.3.0.139
                    +---*---+	            +---*---+
                    |  fir  |               |  ice  |
                    +---*---+               +---*---+
		   eth2 * 10.2.0.143       eth1 * 10.2.0.139
			*			*	
		    *********************************


In case you are wondering, all machines are connected to the same
"main" network with their eth0 interfaces, but this is irrelevant to
the examples, and hence not shown in the diagram.

Only fir and ice need to run IPSEC. 

All netmasks are 255.255.0.0.

Elf has a route to 10.3.xx.xx via fir, and del has a route to
10.1.xx.xx via ice. 

fir and ice know how to route only to their connected subnets; fir
does not (yet) know how to get to 10.3.xx.xx, and ice does not know how to
get to 10.1.xx.xx. 

First, let us set up fir. 


Now, ipsec0 needs to be associated with a real interface. In our case,
we shall associate it with the interface on the 10.2.0.0 subnet, that
is, eth2, because that's where IPSEC'ed traffic will flow. Then we
need to configure the new pseudo interface. Because
there is already a route to subnet 10.2.0.0 using eth2, we also need
to remove than and let the ipsec0 interface handle it:

	fir# tncfg attach ipsec0 eth2
	fir# ifconfig ipsec0 10.2.0.143 netmask 255.255.0.0 
	fir# route del 10.2.0.0
	fir# route add -net 10.2.0.0 netmask 255.255.0.0 dev ipsec0

On ice, just load the module.

2.1. Transport Mode.

Let us have fir and ice communicate securely, using the latest and
greatest IPSEC transform: triple-DES with replay protection and
96-bits of MD5 hash.

Issue the following command, which tells fir to process packets
originating with it and destined for ice by applying a transform
defined by destination address 10.2.0.139 (ice) and SPI 125

	fir# addrt 10.2.0.143 255.255.255.255 10.2.0.139 255.255.255.255 \
 		10.2.0.139 125

To verify it has worked, type:

	fir# cat /proc/net/ipsec-rt

you should get:

	(10.2.0.143/255.255.255.255 -> 10.2.0.139/255.255.255.255) =>
		(10.2.0.139, 0x00000115)

To set the actual Security Association, type:

	fir# setsa 10.2.0.139 125 esp 3des-md5-96 i \
		 1000000000000001 6630663066303132

And type the same thing on ice, so it will know how to decrypt packets:

	ice# setsa 10.2.0.139 125 esp 3des-md5-96 i \
		 1000000000000001 6630663066303132

If you ping ice from fir, and look at the traffic on the wire, you'll
see that packets from fir to ice are encrypted (and authenticated),
while packets from ice to fir are in the clear. Needless to say, you
can set up a symmetric set of transforms on ice and fir,
repspectively, so that the reverse traffic is also encrypted.

2.2. Tunnel mode.

Now, we want to set up fir so that packets from elf to del will be
tunneled through the (fir->ice) tunnel. The first step is to set up a
route to net 10.3.xx.xx through the ipsec0 interface:


	fir# route add -net 10.3.0.0 netmask 255.255.0.0 dev ipsec0 gw
10.2.0.139

[ To understand what this does, remember that we "attached" eth2 to
ipsec0; the route is set up so that packets will be routed through
ice, but they will first pass through the ipsec0 interface; then, when
they have been processed, they will be passed on to the attached
interface and delivered to the next-hop specified in the gw parameter
in the route command. ]

Now, issue the following command:

	fir# addrt 10.1.0.0 255.255.0.0 10.3.0.0 255.255.0.0 10.2.0.139 103

To verify it has worked, type:

	fir# cat /proc/net/ipsec-rt

you should get:

(10.1.0.0/255.255.0.0 -> 10.3.0.0/255.255.0.0) => (10.2.0.139, 0x00000103)


This means that packets originating from net 10.1.xx.xx and destined
for net 10.3.xx.xx should be IPSEC-processed, with a "Destination
Address" of 10.2.0.139 and a "Security Parameters Index" of 103. The
Destination Address indicates the other point of the tunnel, whether
it is a real tunnel (as in this case), or simply the destination (in
what we call "transport mode" which doesn't quite work yet). The
Security Parameters Index, or SPI, is an opaque value that indicates,
along with the DA, what processing these packets will receive at our
end as well as the remote end. The pair (DA, SPI) is called a SAID
(Security Association IDentifier) in this document.

We now want to tell the IPSEC code what the processing for packets
which have been selected to be processed with DA=10.2.0.139 and
SPI=103. First, they will be encapsulated in simple IP-in-IP (proto 4)
encapsulation, and to enable that we type:

	fir# setsa 10.2.0.139 103 ip4 10.2.0.143 10.2.0.139

This tells the IPSEC code that packets which have been selected to be
processed with DA=10.2.0.139 and SPI=103 should be run through algorithm
1 (IP-in-IP), with "outer" (encapsulating packet) source and
destination addresses of 10.2.0.143 (fir) and 10.2.0.139 (ice)
respectively. Type
	
	fir# cat /proc/net/ipsec-spi

to verify that the SAID has been formed. You should get

(10.2.0.139, 00000103, 1: [10.2.0.143 -> 10.2.0.139])

So far so good, but we've simply reproduced already existing
functionality. Now, let's add security. First, we'll tell the code to
encrypt packets using the ESP-DES-CBC transform. We'll create another
SAID, this time for algorithm 4 (ESP-DES-CBC).

	fir# setsa 10.2.0.139 105 esp des-cbc 66306630 6630663066303132

This tells the IPSEC layer that packets destined to be processed with
DA=10.2.0.139, SPI=105, should be processed with algorithm #4
(ESP-DES-CBC), use 0x66306630 as the DES-CBC Initialization Vector,
and use 0x6630663066303132 as the DES key (the DES parity bits are
ignored, so this yields the 56-bit DES key). 

Finally, we also want to authenticate the resulting packet, so we
create another SAID, this time for the AH-MD5 transform:

	fir# setsa 10.2.0.139 106 ah md5 66306630663031326630663066303132

Now comes the crucial step. What the original addrt command did was to
establish that outgoing packets are to be processed with IP-in-IP
encapsulatino first. Now, we need to "link" this transform (IPIP) to the ESP
transform and then the AH. We do that with the spigrp ("group SPIs")command:

	fir# spigrp 10.2.0.139 103 10.2.0.139 105 10.2.0.139 106

Now, we also need to specify what will happen when we receive
packets. IP-in-IP does not need any special handling. ESP and AH,
however, need the SAIDs to be established. We use the same commands we
used for the outgoing packets, but specifying ourselves as the
destination (of course). 

	fir# setsa 10.2.0.143 115 esp des-cbc 66306630 6630663066303132
	fir# setsa 10.2.0.143 116 ah md5 66306630663031326630663066303132

To see the whole picture, type:
	fir# cat /proc/net/ipsec-spi
	(10.2.0.143, 00000116, 2: klen = 16, alen = 16)
	(10.2.0.143, 00000115, 4: ivlen = 4, iv = 66 30 66 30)
	(10.2.0.139, 00000106, 2: klen = 16, alen = 16)
	(10.2.0.139, 00000105, 4: ivlen = 4, iv = 66 30 66 30)
	(10.2.0.139, 00000103, 1: [10.2.0.143 -> 10.2.0.139])

On ice, now, we have to send things up the opposite way. Here are the
commands to use:

	ice# ifconfig ipsec0 10.2.0.139 netmask 255.255.0.0
	ice# route add -net 10.1.0.0 netmask 255.255.0.0 dev ipsec0

	ice# addrt 10.3.0.0 255.255.0.0 10.1.0.0 255.255.0.0 10.2.0.143 113
	ice# setsa 10.2.0.143 113 ip4 10.2.0.139 10.2.0.143
	ice# setsa 10.2.0.143 115 esp des-cbc 66306630 6630663066303132
	ice# setsa 10.2.0.143 116 ah md5 66306630663031326630663066303132

	ice# spigrp 10.2.0.143 113 10.2.0.143 115 10.2.0.143 116

	ice# setsa 10.2.0.139 105 esp des-cbc 66306630 6630663066303132
	ice# setsa 10.2.0.139 106 ah md5 66306630663031326630663066303132

	ice# cat /proc/net/ipsec-rt 
	(10.3.0.0/255.255.0.0 -> 10.1.0.0/255.255.0.0) => (10.2.0.143, 0x00000113)
	ice# cat /proc/net/ipsec-spi 
	(10.2.0.143, 00000116, 2: klen = 16, alen = 16)
	(10.2.0.143, 00000115, 4: ivlen = 4, iv = 6f 30 66 30)
	(10.2.0.143, 00000113, 1: [10.2.0.139 -> 10.2.0.143])
	(10.2.0.139, 00000106, 2: klen = 16, alen = 16)
	(10.2.0.139, 00000105, 4: ivlen = 4, iv = 66 30 66 30)

If you ping del from elf, ICMP packets will leave elf, reach fir, get
encapsulated in IPIP, encrypted with DES and authenticated with MD5,
tunneled to ice, get decapsulated, and then sent to del; the return
packets will follow the inverse path.

For completeness, let us show part of the routing tables on all four machines:

fir# netstat -r -n
Kernel routing table
Destination     Gateway         Genmask         Flags Metric Ref Use    Iface
<my-home-net>   0.0.0.0         255.255.255.128 U     0      0       32 eth0
10.1.0.0        0.0.0.0         255.255.0.0     U     0      0        2 eth1
10.2.0.0        0.0.0.0         255.255.0.0     U     0      0        3 eth2
10.3.0.0        0.0.0.0         255.255.0.0     U     0      0        2 ipsec0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        4 lo

ice# netstat -r -n
Kernel routing table
Destination     Gateway         Genmask         Flags Metric Ref Use    Iface
<my-home-net>   0.0.0.0         255.255.255.128 U     0      0       10 eth0
10.2.0.0        0.0.0.0         255.255.0.0     U     0      0        1 eth1
10.3.0.0        0.0.0.0         255.255.0.0     U     0      0        2 eth2
10.1.0.0        0.0.0.0         255.255.0.0     U     0      0        1 ipsec0
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        1 lo

elf$ netstat -r -n
Kernel routing table
Destination     Gateway         Genmask         Flags Metric Ref Use    Iface
<my-home-net>   0.0.0.0         255.255.255.128 U     0      0       11 eth0
10.1.0.0        0.0.0.0         255.255.0.0     U     0      0        1 eth1
10.3.0.0        10.1.0.143      255.255.0.0     UG    0      0        1 eth1
127.0.0.0       0.0.0.0         255.0.0.0       U     0      0        1 lo

del$ netstat -r -n
<...>
Destination      Gateway            Flags     Refs     Use  Interface
10.1/16          10.3.0.139         UGS         0      613  ne1
10.3/16          link#1             UC          0        0  ne1
<...>

(del is a BSD machine).


*
* $Log: ji_setup.txt,v $
* Revision 1.6  1999/04/06 04:54:23  rgb
* Fix/Add RCSID Id: and Log: bits to make PHMDs happy.  This includes
* patch shell fixes.
*
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