Fix Virtual DHCP Server: Correct DHCP Sequence

[hiura2023]

Changes proposed in this pull request:

• Virtual DHCP sequence is not correct.
  Why does DHCP NAK respond to DHCP DISCOVER ?

• Change DHCP sequence like below.

• Actual action
  ①DHCP DISCOVER
  ②DHCP NAK
  ③DHCP DISCOVER
  ④DHCP NAK
  ⑤Sequence ③,④ repeated several times.
  ⑥DHCP DISCOVER
  ⑦DHCP OFFER
  ⑧DHCP REQUEST
  ⑨DHCP ACK
  Attached A and B

• Expected action
  ①DHCP DISCOVER first
  ②DHCP DISCOVER second
  ③DHCP DISCOVER repeated several times
  ④DHCP OFFER
  ⑤DHCP REQUEST
  ⑥DHCP ACK
  DHCP client resend ②,③ if VPN server is not ready to reply ④ immediately
  Refer to RFC2131

• Ideal action
  ①DHCP DISCOVER
  ②DHCP OFFER
  ③DHCP REQUEST
  ④DHCP ACK

Refer to RFC2131:
https://www.rfc-editor.org/rfc/rfc2131#section-4.4
[Page 34]Figure 5: State-transition diagram for DHCP clients

Timeout example:
https://www.cente.jp/files/20100222_TCPIPv4_001-0016.pdf

Attached A:
The time-out period is 20 seconds on "security policy of user" screen.

Attached B:
SEVPN_DHCP_TOO_LATE_REMOTE.txt

[chipitsine]

How do you find all those ? Just curious

…

On Fri, Apr 26, 2024, 08:40 hiura2023 ***@***.***> wrote: Changes proposed in this pull request: - Virtual DHCP does not work. - Change DHCP sequence like below. - Actual action ①DHCP DISCOVER ②DHCP NAK ③DHCP DISCOVER ④DHCP NAK ⑤Repeat it (same as ③,④) - Expected action ①DHCP DISCOVER first ②DHCP DISCOVER second ③DHCP DISCOVER n times ④DHCP OFFER ⑤DHCP REQUEST ⑥DHCP ACK ------------------------------ You can view, comment on, or merge this pull request online at: #1989 Commit Summary - 7f074d0 <7f074d0> Fix Virtual DHCP Server: Correct HDCP Sequence - 6227919 <6227919> Merge branch 'SoftEtherVPN:master' into master File Changes (1 file <https://github.com/SoftEtherVPN/SoftEtherVPN/pull/1989/files>) - *M* src/Cedar/Virtual.c <https://github.com/SoftEtherVPN/SoftEtherVPN/pull/1989/files#diff-1e6764240341846ba3ea52a6a7bf68bf5713dc5818eee5c82479ad4b8bbce879> (56) Patch Links: - https://github.com/SoftEtherVPN/SoftEtherVPN/pull/1989.patch - https://github.com/SoftEtherVPN/SoftEtherVPN/pull/1989.diff — Reply to this email directly, view it on GitHub <#1989>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AAQ5KUEXFOHRLVDHBDI25YTY7HZGBAVCNFSM6AAAAABG2GPHYKVHI2DSMVQWIX3LMV43ASLTON2WKOZSGI3DKMBWHA3TINY> . You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>

[hiura2023]

I updated first comment.

I think that DHCP_NAK responds to DHCP_REQUEST, not DHCP_DISCOVER.
Refer to RFC2131.
Who added virtual DHCP server ? Ask him.

[hiura2023]

How do you find all those ? Just curious

I added the test environment and test result later.
find what ?

[chipitsine]

How do you find all those ? Just curious

I added the test environment and test result later. find what ?

I've some ideas on automated testing.

in theory we can try ISC dhclient, which is flexible and allows dhclient-script to handle response instead of applying to system live. but those are ideas for future improvements

[hiura2023]

Description of second pull request I added

0. The second pull request applies to fixed IP address assignment using the user's "note" field.
1. Reassigning static IP address does not work.
2. I changed the way of assigning static IP address to work.
3. As to the issue, refer to
   [Bug] SecureNAT DHCP does not give any IP address, if client is re-connecting, and if set to Fixed IPv4: #1947

Ideal action

①DHCP DISCOVER
②DHCP OFFER
③DHCP REQUEST
④DHCP ACK
⑤DHCP REQUEST FOR RENEWAL LEASE TIME 1
⑥DHCP ACK
⑦DHCP REQUEST FOR RENEWAL LEASE TIME 2
⑧DHCP ACK
⑨DHCP REQUEST FOR RENEWAL LEASE TIME 3
⑩DHCP ACK
CONTINUED

Attached A:

Lease Limit:40 seconds
DisableSessionReconnect: true
Time-out Period: 20 seconds

[PizzaProgram]

@hiura2023 Excellent work!

I've checked the code changes and as much as I understood it's perfect!
(I'm not a C expert, only Delphi but your coding is very nice and understandable. Special thanks for the inserted comments! )

If this Commit will be applied,

• FIXed IPs MUST be outside of the normal DHCP range. Right ?

[chipitsine]

thank you for contribution!

[chipitsine]

I'm going to make a release today