Cisco ASR1K - 100M link issue. [SOLVED]

I was labbing today and hit one strange issue - a link between Cisco ASR1001-X (GLC-T transceiver) and Catalyst 3750 switch (100Mbps ports) was up at both sides, but CDP didn’t work, I didn’t see MAC addresses learned on the switch side. To fix an issue I had to disable auto-negotiation and hardcode 100M speed on ASR side.

interface GigabitEthernet0/0/0
 no negotiation auto
 speed 100

Even more, on Catalyst side I had to hardcode “duplex full” to get rid of duplex mismatch issue. Looks like it’s an issue with ASR or a transceivers. Anyways, it’s strange and annoying to see the link UP on both ends, but without actual connectivity:

Good luck!

Cisco ASA - crypto ipsec df-bit clear-df. [TESTED]

When you use Cisco ASA to build a VPN you better make sure that you’re passing packets with max size with DF-bit enabled. Here is the way to do it:

crypto ipsec df-bit clear-df outside

Before:

Router#ping vrf TEST 1.1.1.1 size 1500 df-bit
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
Packet sent with the DF bit set
M.M.M
Success rate is 0 percent (0/5)
Router#

“M” means “Could not fragment.”

After:

Router#ping vrf TEST 1.1.1.1 size 1500 df-bit
Type escape sequence to abort.
Sending 5, 1500-byte ICMP Echos to 1.1.1.1, timeout is 2 seconds:
Packet sent with the DF bit set
.!!!!
Router#

Good luck!

How to figure out your IPv4 public IP from CLI (using TELNET). [TESTED]

This thing is known for decades, but the whole purpose of this post is for me to memorize new test public FTP server that I can use - speedtest.tele2.net [90.130.70.73]. The one that I used before for years is not working anymore.

All you need to do it so use any TELNET client (PuTTY for example). The only thing I noticed is when you use PuTTY you have to hit ENTER to get the prompt, then you can do user, pass, stat…

All you have to do is this:

telnet speedtest.tele2.net 21

user ftp
pass ftp
stat

!!! You should see your public IP here !!!

quit

Here is an example:

C:>telnet speedtest.tele2.net 21

220 (vsFTPd 3.0.3)
user ftp
331 Please specify the password.
pass ftp
230 Login successful.
stats
500 Unknown command.
stat
211-FTP server status:
     Connected to ::ffff:123.4.5.6
     Logged in as ftp
     TYPE: ASCII
     No session bandwidth limit
     Session timeout in seconds is 300
     Control connection is plain text
     Data connections will be plain text
     At session startup, client count was 58
     vsFTPd 3.0.3 - secure, fast, stable
211 End of status
quit
221 Goodbye.

Good luck!

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