Configuring a Cisco 877 in full bridge mode
Accessing the device
When sshing into this device with a recent version of ssh you may need to use this command:
ssh -o HostKeyAlgorithms=ssh-rsa,ssh-dss -o KexAlgorithms=diffie-hellman-group1-sha1 \ -o Ciphers=aes128-cbc,3des-cbc -o MACs=hmac-md5,hmac-sha1 admin@192.168.0.1
As there is a bug here and here with new versions of OpenSSH and Cisco's old sshd.
Enabling SSH
If you do not have SSH access to your modem you may need to enable it. The > represents regular "user" mode while # on the terminal represents "privileged". Think of it like "su".
router>enable Password: router#configure terminal Enter configuration commands, one per line. End with CNTL/Z. router(config)#ip domain-name <YOUR DOMAIN>
Make sure to say you want 2048 bits or the router will fall back to ssh 1 and won't allow you to have ssh 2
router(config)#crypto key generate rsa The name for the keys will be: router.<YOUR DOMAIN> Choose the size of the key modulus in the range of 360 to 2048 for your General Purpose Keys. Choosing a key modulus greater than 512 may take a few minutes. How many bits in the modulus [512]: 2048 % Generating 2048 bit RSA keys, keys will be non-exportable... router(config)#ip sh version 2
Uploading a configuration file to the router
There are a number of ways of doing this. You can use tftp (trivial ftp) or ssh.
From a server running a sshd
If you have a server running a sshd you can copy the configuration file from that server over your running-config
copy running-config scp://user:password@ip/filename
Enabling the scp server on the modem
router(config)#ip scp server enable router(config)#aaa new-model router(config)#aaa authentication login default local router(config)#aaa authorization exec default local none router(config)#username USER privilege 15 password <USER PASSWORD CLEARTEXT> router(config)#ip scp server enable
Then from your Linux workstation you can upload the configuration file.
The startup-config is the one the modem loads from nvram on boot:
scp admin@192.168.0.1:nvram:startup-config .
The running-config is the one the modem uses that is in memory:
scp admin@192.168.0.1:system:running-config .
Using minicom over serial
If you're completely locked out of your Cisco router you may need to use the serial cable.
For this you can use minicom, the settings you will need to connect to the modem
pu port /dev/ttyUSB0 pu baudrate 9600 pu bits 8 pu parity N pu stopbits 1
Note you'll have to change the serial line to whatever it is on your computer. I used a USB to serial dongle because I have no serial ports.
Configuration of a Cisco 877 ADSL Modem
! version 12.4 no service pad service timestamps debug datetime msec service timestamps log datetime msec service password-encryption ! hostname <HOSTNAME> ! boot-start-marker boot-end-marker ! logging message-counter syslog logging buffered 4096 informational enable secret 5 <SECRET> ! aaa new-model ! ! aaa authentication login default local aaa authentication login local_auth local aaa authorization exec default local none ! ! aaa session-id common ! ! dot11 syslog ip source-route no ip routing ! ! ! ! no ip cef ip domain name <DOMAIN NAME> no ipv6 cef ! multilink bundle-name authenticated ! ! ! username admin privilege 15 secret 5 <SECRET> username USER privilege 15 password 7 <SECRET> ! ! ! archive log config hidekeys ! ! ip ssh version 2 ip scp server enable ! bridge irb ! ! interface ATM0 no ip address no ip route-cache no atm ilmi-keepalive pvc 8/35 encapsulation aal5snap ! bridge-group 1 ! interface FastEthernet0 ! interface FastEthernet1 ! interface FastEthernet2 ! interface FastEthernet3 ! interface Dot11Radio0 no ip address no ip route-cache shutdown speed basic-1.0 basic-2.0 basic-5.5 6.0 9.0 basic-11.0 12.0 18.0 24.0 36.0 48.0 54.0 station-role root ! interface Vlan1 no ip address no ip route-cache bridge-group 1 ! interface BVI1 ip address 192.168.0.1 255.255.255.252 no ip route-cache ! ip default-gateway 192.168.0.2 ip default-network 192.168.0.0 ip forward-protocol nd no ip http server no ip http secure-server ! ! ! ip access-list standard SSH_ACCESS !This is a list of the addresses you want to allow permit <IP> permit <IP> ! ! ! ! ! ! control-plane ! bridge 1 protocol ieee bridge 1 route ip banner login Authorized access only! Disconnect IMMEDIATELY if you are not an authorized user! ! line con 0 no modem enable line aux 0 line vty 0 4 access-class SSH_ACCESS in authorization exec local_author login authentication login_local transport input ssh ! scheduler max-task-time 5000 end
Besides changing the obvious things such as the hostname, domain name, and permitted IPs, you'll also need to verify the ATM0 settings match your ISP's configuration. Specifically: "pvc 8/35" and "encapsulation aal5snap" works for me but may not for you. You will also need to generate the passwords and replace all the instances of <SECRET>.
Generating the passwords
Secret 5 Password
You can generate the hash for the "secret 5" passwords with this OpenSSL command:
openssl passwd -salt `openssl rand -base64 3` -1 "<YOUR PASSWORD>"
Put the output in <SECRET>
Secret 7 Password
To encrypt the secret 7 password you can use this perl script thanks to m00nie.
#!/usr/bin/perl
# Cisco (type 7) password tool from www.m00nie.com :D
# Will either decrypt a _TYPE 7_ password from a cisco device
# or will encrypt a string so that it can be used in a cisco
# device.
#
# I made this code to learn more Perl and just out of interest
# about the type 7 "encryption". The decryption code is already
# and from a mailing list. The original header from that is below.
#
# Credits for original code and description hobbit@avian.org,
# SPHiXe, .mudge et al. and for John Bashinski <jbash@CISCO.COM>
# for Cisco IOS password encryption facts.
#
# Use for any malice or illegal purposes strictly prohibited!
#
@xlat = ( 0x64, 0x73, 0x66, 0x64, 0x3b, 0x6b, 0x66, 0x6f, 0x41,
0x2c, 0x2e, 0x69, 0x79, 0x65, 0x77, 0x72, 0x6b, 0x6c,
0x64, 0x4a, 0x4b, 0x44, 0x48, 0x53 , 0x55, 0x42 );
$loop = 0;
while ($loop == 0) {
print "\n\n***************************************************************\n";
print "* Cisco (type 7) password tool from www.m00nie.com :D *\n";
print "* Use for any malice or illegal purposes strictly prohibited! *\n";
print "***************************************************************\n\n";
print "1. Decrypt a password\n";
print "2. Encrypt plain text\n";
print "3. Quit\n\n";
print "Pick either 1, 2 or 3: ";
chomp ($choice = <STDIN>);
if ( $choice == 1 ) {
decrypt()
} elsif ( $choice == 2) {
encrypt()
} elsif ($choice == 3) {
exit
} else {
print "$choice is not a valid option\n";
}
}
sub decrypt {
print "Enter the encrypted password: ";
chomp ($epass = <STDIN>);
if (!(length($epass) & 1)) {
$ep = $epass;
$dpass = "";
($s, $e) = ($ep =~ /^(..)(.+)/);
for ($i = 0; $i < length($e); $i+=2){
$dpass .= sprintf "%c",hex(substr($e,$i,2))^$xlat[$s++];
}
}
print "\nEncrypted pass was: $epass\n";
print "Decrypted pass is: $dpass\n";
}
sub encrypt {
print "Enter the string to encrypt:\n";
chomp ($ptext = <STDIN>);
$pt = $ptext;
$etext = "";
$n = 2;
$etext .= sprintf("%.2o", $n);
for ($k = 0; $k < length($pt); $k+=1){
$tmp = ord(substr($pt,$k,1))^$xlat[$n++];
$etext .= sprintf("%.2X", $tmp);
}
print "\nPlain string was: $ptext\n";
print "Encrypted string is: $etext\n";
}
# eof