Hello All, I am working on the requirement to allow underscores in HTTP headers by default F5 does not allow it. Can anybody let me know what I need to do at the F5 end to allow underscores like writing a iRule? If I need to write an iRule what I need to check as I am very new to Load Ba lancer world? Any help is greatly appreciated!!

what part of the F5 BIG-IP does not allow them? in general you see different kind of products not really liking underscores in HTTP header although the RFC doesn't disallow them. perhaps it would be better to stay away from them. as for iRule just browse here, there are many good articles on them. but first explain your need a bit better.

All you need to do to make this load balance properly is to apply a cookie persistence profile to your virtual server. In the virtual server you can configure it to insert X-Forwarded-For header as the URL requires. You do not need any special headers to achieve what that document describes.

Thanks for the response ekaleido. https://www.ibm.com/support/knowledgecenter/SSRQBP_2.0.2/com.ibm.ispim.doc/installing/ref/r_load_balancer_settings.html As mentioned in the URL it's a virtual appliance on which internally IBM HTTP server is running but virtual appliance is kind of black box thing where we can't make any changes to the web server or application server so whatever load balancer requirement are there we have to implement on the load balancer side. Can you please help how can I implement the requirements on load balancer side? We are able to insert X-Forwarded-For header but facing challenges to allow underscores in the request headers?

How to Allow Underscore in HTTP Header?

boneyard
MVP
Jul 22, 2016
what part of the F5 BIG-IP does not allow them?

in general you see different kind of products not really liking underscores in HTTP header although the RFC doesn't disallow them. perhaps it would be better to stay away from them.

as for iRule just browse here, there are many good articles on them. but first explain your need a bit better.
ekaleido_26616
Cirrocumulus
Jul 22, 2016
All you need to do to make this load balance properly is to apply a cookie persistence profile to your virtual server. In the virtual server you can configure it to insert X-Forwarded-For header as the URL requires. You do not need any special headers to achieve what that document describes.
- joyharry_281042
  Nimbostratus
  Jul 22, 2016
  Thanks for the response ekaleido.
  
  https://www.ibm.com/support/knowledgecenter/SSRQBP_2.0.2/com.ibm.ispim.doc/installing/ref/r_load_balancer_settings.html
  
  As mentioned in the URL it's a virtual appliance on which internally IBM HTTP server is running but virtual appliance is kind of black box thing where we can't make any changes to the web server or application server so whatever load balancer requirement are there we have to implement on the load balancer side. Can you please help how can I implement the requirements on load balancer side? We are able to insert X-Forwarded-For header but facing challenges to allow underscores in the request headers?
- ekaleido_26616
  Cirrocumulus
  Jul 22, 2016
  Underscores in headers are fine by the F5. I've copied a link showing this in a packet capture:
  ¬†
  
  https://devcentral.f5.com/s/feed/0D51T00006i7X5xSAE
  ¬†
- joyharry_281042
  Nimbostratus
  Sep 08, 2016
  Thanks all for your support.
  
  Issue has been resolved. Underscores are allowed by default in F5, no specific configuration is required to achieve to allow underscores.
  
  Thanks!!
ekaleido
Cirrus
Jul 22, 2016
All you need to do to make this load balance properly is to apply a cookie persistence profile to your virtual server. In the virtual server you can configure it to insert X-Forwarded-For header as the URL requires. You do not need any special headers to achieve what that document describes.
- joyharry_281042
  Nimbostratus
  Jul 22, 2016
  Thanks for the response ekaleido.
  
  https://www.ibm.com/support/knowledgecenter/SSRQBP_2.0.2/com.ibm.ispim.doc/installing/ref/r_load_balancer_settings.html
  
  As mentioned in the URL it's a virtual appliance on which internally IBM HTTP server is running but virtual appliance is kind of black box thing where we can't make any changes to the web server or application server so whatever load balancer requirement are there we have to implement on the load balancer side. Can you please help how can I implement the requirements on load balancer side? We are able to insert X-Forwarded-For header but facing challenges to allow underscores in the request headers?
- ekaleido
  Cirrus
  Jul 22, 2016
  Underscores in headers are fine by the F5. I've copied a link showing this in a packet capture:
  
  https://devcentral.f5.com/questions/httpheader-insert-cannot-insert-header-with-an-underscore-in-the-name
- joyharry_281042
  Nimbostratus
  Sep 08, 2016
  Thanks all for your support.
  
  Issue has been resolved. Underscores are allowed by default in F5, no specific configuration is required to achieve to allow underscores.
  
  Thanks!!
Jinshu
Cirrus
Jul 22, 2016
Even I think the same.

underscores in request headers are default allowed as per RFC but uncommon. You need to enable it in the server side and i dont think any changes required on F5 BIG IP.

-Jinshu
boneyard
MVP
Jul 22, 2016
is this the line that worries you joyharry?

Set the Load Balancer to allow underscores in request headers. For example, set the value of the underscores_in_headers custom header directive to on in Nginx.

as mentioned by a few people now the F5 does allow this, if you feel differently please show us where it says it doesn't work.