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TTL in DNS caches MSR

 
Occasional Contributor

TTL in DNS caches MSR

We have the following DNS Server configuration with the MSR3012 with IP and DNS given by DHCP. The HPE_1 and HPE_2 devices are linked to level 3 on a point-to-point ip interface: 

CONFIG HPE_1

 

interface g0/0

ip address 192.168.134.1 255.255.255.0

no proxy-arp enable

no ip irdp

exit

interface g0/1

ip address 1.1.1.1 255.255.255.252

no proxy-arp enable

no ip irdp

exit

dns domain Prueba

dns server 1.1.1.2

ip host server_1 2.2.2.2

ip host server_2 3.3.3.3

ip host dns1 1.1.1.1

dhcp server ip-pool 1

network 192.168.134.0 mask 255.255.255.0

expired day 10 hour 12

domain-name Prueba

dns-list 192.168.134.1 1.1.1.2

gateway-list 192.168.134.1

quit        

ip route-static 2.2.2.2 255.255.255.255 1.1.1.2

ip route-static 3.3.3.3 255.255.255.255 1.1.1.2

 

 

CONFIG HPE_2

 

interface g0/0

ip address 1.1.1.2 255.255.255.252

no proxy-arp enable

no ip irdp

exit

dns domain Prueba

ip host dns2 1.1.1.2

interface LoopBack 1

description server_1

ip address 2.2.2.2 32

undo shutdown

exit

interface LoopBack 2

description server_2

ip address 3.3.3.3 32

undo shutdown

exit

ip route-static 192.168.134.0 255.255.255.0 1.1.1.1

 

 

HPE 1

[HPE_1]display dns host

Type:

  D: Dynamic    S: Static

 

Total number: 3

No.  Host name               Type  TTL        Query type  IP addresses

1    dns1                    D     3412       A           1.1.1.1            

2    dns2                    D     2582       A           1.1.1.2            

3    server_1                D     3521       A           2.2.2.2  

 

[HPE_1]ping server_2

Ping server_2 (3.3.3.3): 56 data bytes, press CTRL_C to break

56 bytes from 3.3.3.3: icmp_seq=0 ttl=255 time=0.320 ms

*Jun 15 23:35:16:864 2017 HPE_1 DNS/7/EVENT: Starting A resolving for server_2

*Jun 15 23:35:16:864 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2 in local database

*Jun 15 23:35:16:864 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2.Prueba in dynamic cache

*Jun 15 23:35:16:864 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2 in dynamic cache

*Jun 15 23:35:16:864 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2.Prueba by contacting DNS server 1.1.1.2 through UDP

*Jun 15 23:35:16:865 2017 HPE_1 DNS/7/PACKET: Sent:

Header:

ID = 26934

QR = 0, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:35:16:865 2017 HPE_1 DNS/7/PACKET: Sent:

Question:

QName  = server_2.Prueba

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:35:16:865 2017 HPE_1 DNS/7/EVENT: Waiting 2 seconds for server response

*Jun 15 23:35:16:866 2017 HPE_1 DNS/7/PACKET: Received:

Header:

ID = 26934

QR = 1, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 2

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:35:16:866 2017 HPE_1 DNS/7/PACKET: Received:

Question:

QName  = server_2.Prueba

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:35:16:866 2017 HPE_1 DNS/7/EVENT: Received an answer: QName = server_2.Prueba, ID = 26934

*Jun 15 23:35:16:866 2017 HPE_1 DNS/7/EVENT: The answer is invalid.

*Jun 15 23:35:16:866 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2 by contacting DNS server 1.1.1.2 through UDP

*Jun 15 23:35:16:867 2017 HPE_1 DNS/7/PACKET: Sent:

Header:

ID = 32495

QR = 0, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:35:16:867 2017 HPE_1 DNS/7/PACKET: Sent:

Question:

QName  = server_2

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:35:16:867 2017 HPE_1 DNS/7/EVENT: Waiting 2 seconds for server response

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/PACKET: Received:

Header:

ID = 32495

QR = 1, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 1

NSCount = 0

ARCount = 0

 

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/PACKET: Received:

Question:

QName  = server_2

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/PACKET: Received:

Answer:

Name     = server_2

Type     = A (1)

Class    = IN (1)

TTL      = 3600

RDLength = 4

RData    = 3.3.3.3

 

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/EVENT: Received an answer: QName = server_2, ID = 32495

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2 in dynamic cache

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/EVENT: Added a dynamic DNS entry server_2

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/EVENT: Successfully resolved server_2: host name is server_2, address is 3.3.3.3

*Jun 15 23:35:16:868 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2.Prueba in dynamic cache

*Jun 15 23:35:16:869 2017 HPE_1 DNS/7/EVENT: Trying to resolve server_2 in dynamic cache

56 bytes from 3.3.3.3: icmp_seq=1 ttl=255 time=0.286 ms

56 bytes from 3.3.3.3: icmp_seq=2 ttl=255 time=0.235 ms

56 bytes from 3.3.3.3: icmp_seq=3 ttl=255 time=0.262 ms

56 bytes from 3.3.3.3: icmp_seq=4 ttl=255 time=0.239 ms

 

--- Ping statistics for server_2 ---

5 packet(s) transmitted, 5 packet(s) received, 0.0% packet loss

round-trip min/avg/max/std-dev = 0.235/0.268/0.320/0.032 ms

[HPE_1]%Jun 15 23:35:17:673 2017 HPE_1 PING/6/PING_STATISTICS: Ping statistics for server_2: 5 packet(s) transmitted, 5 packet(s) received, 0.0% packet loss, round-trip min/avg/max/std-dev = 0.235/0.268/0.320/0.032 ms.

 

 

 

------------------------------------------------------------------------------------------------------------------

 

HPE 2

 

[HPE_2]

*Jun 15 23:33:20:659 2017 HPE_2 DNS/7/PACKET: Received:

Header:

ID = 26934

QR = 0, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:33:20:659 2017 HPE_2 DNS/7/PACKET: Received:

Question:

QName  = server_2.Prueba

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: DNS proxy received a request for resolving server_2.Prueba

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: Trying to resolve server_2.Prueba in local database

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: Trying to resolve server_2.Prueba in dynamic cache

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: No DNS server is found.

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: Failed to resolve server_2.Prueba

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: DNS proxy sent a reply for resolving server_2.Prueba

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/PACKET: Sent:

Header:

ID = 26934

QR = 1, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 2

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/PACKET: Sent:

Question:

QName  = server_2.Prueba

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: Trying to resolve server_2.Prueba in dynamic cache

*Jun 15 23:33:20:660 2017 HPE_2 DNS/7/EVENT: Trying to resolve server_2.Prueba.Prueba in dynamic cache

*Jun 15 23:33:20:661 2017 HPE_2 DNS/7/PACKET: Received:

Header:

ID = 32495

QR = 0, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 0

NSCount = 0

ARCount = 0

 

*Jun 15 23:33:20:661 2017 HPE_2 DNS/7/PACKET: Received:

Question:

QName  = server_2

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:33:20:661 2017 HPE_2 DNS/7/EVENT: DNS proxy received a request for resolving server_2

*Jun 15 23:33:20:661 2017 HPE_2 DNS/7/EVENT: Trying to resolve server_2 in local database

*Jun 15 23:33:20:661 2017 HPE_2 DNS/7/EVENT: DNS proxy sent a reply for resolving server_2

*Jun 15 23:33:20:662 2017 HPE_2 DNS/7/PACKET: Sent:

Header:

ID = 32495

QR = 1, OpCode = 0, AA = 0, TC = 0, RD = 1

RA = 0, Z = 0, AD = 0, CD = 0, RCode = 0

QDCount = 1

ANCount = 1

NSCount = 0

ARCount = 0

 

*Jun 15 23:33:20:662 2017 HPE_2 DNS/7/PACKET: Sent:

Question:

QName  = server_2

QType  = A (1)

QClass = IN (1)

 

*Jun 15 23:33:20:662 2017 HPE_2 DNS/7/PACKET: Sent:

Answer:

Name     = server_2

Type     = A (1)

Class    = IN (1)

TTL      = 3600

RDLength = 4

RData    = 3.3.3.3

 

 

What maximum lifetime are these DNS entries saved in HPE1, I see that there is a TTL in the display. What ttl have dns resolutions that caches the proxy-dns? Is there a maximum size?

In Debug does not appear the source of the DNS request, how could it be visualized?

 

Regards.