Netmiko find prompt before applying configuration

[kbSean1]

I use Netmiko to ssh to a cisco router and I was trying to apply the BGP configuration using ssh_conn.send_config_set(). Below is a sample configuration to be applied. Expected behavior:
bgp router-id x.x.x.x should be configured under the vrf address family. For some reason, when I tested manually, router didn't change the prompt and hence applied all the configuration to the global mode instead of address family mode and resulted in a BGP flap. Is there any way to check the prompt before applying the configuration?
router bgp as_no
address-family ipv4 vrf {vrf_name}
bgp router-id x.x.x.x

[ktbyers]

@kbSean1 Netmiko will send what you specified via send_config_set().

Do you know why it didn't go into the address-family VRF? Was it because the VRF didn't exist?

You can use the error_pattern feature in send_config_set to cause configuration commands to abort if specific error messages are detected. So you could abort if you failed to enter into the VRF (for example, for a case like the following):

cisco3(config-router)#address-family ipv4 vrf foo 
% VRF foo does not exist.
cisco3(config-router)#

I don't have a document on this, but here is a video I made on this not to long ago:

https://youtu.be/oGtCebtgUio

[kbSean1]

For instance in this example,
When we apply :
R1(config-router)# address-family ipv4 vrf vrf_name
this would change to
R1(config-router-af)#
Is there a way we can find this prompt before applying next commands?

[ktbyers]

Sure you can write a custom function using write_channel and read_channel and pattern match based on that.

I also just put in the develop branch a send_command_multiline which allows you to send a series of commands and corresponding expected patterns:

    commands = ( 
        ("ping", r"ip"),
        ("", r"Target IP address"),
        ("8.8.8.8", "Repeat count"),
        ("100", "Datagram size"),
        ("", "Timeout in seconds"),
        ("", "Extended"),
        ("", "Sweep"),
        ("", ""),
    )   
    output = net_connect.send_multiline(commands)

The first element of the tuple is a command to send. The second element is the pattern to expect in the output.

If the command is a null-string, then that is equivalent to sending an . If the pattern is a null-string, then it will base the pattern on the prompt.

[kbSean1]

@ktbyers Thanks! When I did some more testing today in the Cisco router, I saw this kind of behavior:

Manual execution results:
R1#conf t
Enter configuration commands, one per line. End with CNTL/Z.
R1(config)#router bgp {as_no}
R1(config-router)#address-family ipv4 vrf VRF_WL
% VRF VRF_WL does not exist.
R1(config-router)#exit
Assuming initial cluster id to be 0.0.16.0,
python code:
config_lines_1 = ["router bgp {as_no}","address-family ipv4 vrf VRF_WL","bgp cluster-id 0.0.17.2"]
output1 = ssh_conn.send_config_set(config_lines_1, error_pattern= r"%.*")
After execution, resulted in the below error.

line 36, in
File "/usr/local/lib/python3.9/site-packages/netmiko/base_connection.py", line 1927, in send_config_set
raise ConfigInvalidException(msg)
netmiko.ssh_exception.ConfigInvalidException: Invalid input detected at command: bgp cluster-id 0.0.17.2
Here the VRF did not exist, but it also applied the cluster-id value to the configuration. Could you point me on what I am doing wrong here? Ideally it shouldn't change the cluster id since the error should be detected after sending the second command, "address-family ipv4 vrf VRF_WL"

[ktbyers]

When you say it also applied, the it here is the Cisco device, not Netmiko:

R1(config-router)#exit
Assuming initial cluster id to be 0.0.16.0,      # This is Cisco doing this

You should be able to verify if you do replicate that behavior manually.

Let me know if you observe something different.

[kbSean1]

@ktbyers I executed it manually and saw that the bgp cluster-id got changed in this case(Which like you mentioned , Cisco is doing ) this one.
But if we use error_pattern feature in send_config_set , it should abort the next lines of configuration, if specific error messages are detected. Right?
I am expecting to see this behavior, where , when I execute the second command, which is address-family ipv4 vrf VRF_WL, the device throws an error, for example, "% VRF VRF_WL does not exist." and then Netmiko should abort next line "bgp cluster-id 0.0.17.2" , from configuring right? Is there any way to solve this issue in Netmiko?

Is there a way to do this using send_multiline(commands)?