Transparent Proxy vs. Reverse Proxy Cache

What is a Transparent Proxy?

A cache/proxy that intercepts requests from users in a transparent manner and serves content from origin/cache without modifying the requests/responses

What is a Reverse Proxy?

A cache/proxy that receives requests destined to certain origin servers and serves content from origin/cache with/without modifying the requests/responses. Both origin and user can be aware of the presence of cache/proxy in-between.

When are the characteristics of a Transparent Proxy Cache?

• Requests are redirected to the cache using Policy Based Routing (PBR) or Filter Based Forwarding (FBF) / Static route modification / WCCP 

• Typically deployed at Internet Service Provider / Enterprise / Campus Edges only

• Requires routing policy changes at all the edge routers/switches that are handling user requests

• Does not require any contracts to be signed with the content publisher 

• Server / Clients do not know about the presence of a cache in-between

When are the characteristics of a Reverse Proxy Cache?

• Requests redirected to the cache using DNS based routing

• Typically deployed at Origin or Content Publisher / CDN Edges. Can also be deployed at Internet Service Provider / Enterprise /Campus edges.

• Requires changes in the DNS Server. Domains have to be modified to point to the cache's IP address.

• May require contracts with the content publisher or content owner

• Server / Client knows about the presence of a cache in-between

What are the advantages of deploying a caching in Transparent Proxy mode?

•  Users need not modify browser/player settings to go through a proxy cache

•  Client & Server are unaware of the presence of a cache in-between (assuming that the cache honors HTTP standards)

•  Commonly used at ISP / Campus Edges

What are the limitations of Transparent Proxy caching?

• Increases load on router/switch to inspect and forward requests to the proxy/cache

• Cache has to be compliant with Digital Millennium Copyright Act (DMCA regulations)

•  Not suitable for CDN or Content Publisher Edges

What are the advantages of a reverse proxy cache?

•  Users need not modify their browser settings to go through a proxy cache

•  Request routing done at the DNS server (centralized configuration change)

•   Commonly used at Origin locations or Content Provider Edges

What are the limitations of a reverse proxy cache?

• Server/Users know about the presence of the cache in-between 

•  DNS entries have to be modified for all the domains (to route the requests to the proxy/cache)

When is a caching appliance deployed as a transparent proxy?

• The customer doesn’t want the users or the origin servers to know about the presence of a proxy/cache
• The customer wants to do caching at the edge
• The customer is an ISP or Campus Edge operator
• The customer doesn’t want its users to modify their browser configuration to point to a proxy
• The customer doesn’t want to change the DNS configuration
• The customer is ready to turn-on Policy Based Routing/Filter Based Forwarding/Static Routing at Edge

When is a caching appliance deployed as a reverse proxy?

• The customer wants to do caching at the origin or  edge
• The customer is a Content Publisher, CDN or a ISP/Campus Edge operator
• The customer doesn’t want its users to modify their browser configuration to point to a proxy
• The customer doesn’t want to change policies or configuration in the routers/switches
• The customer is ready to change DNS configuration
• The customer is OK, if the user/origin knows about the presence of a proxy/cache in-between