percent sign
The percent sign only occurs within routing tables. It indicates a QoS value, and is used to determine routing priorities in the case where several traffics are competing for the bandwidth of the same hardware interface. It should not dertermine the target of the routing, and should not impact the incoming trafic (except in the case where the incoming traffic can't be fully stored in local buffers, in which case, the value may be determined to drop some other packets with lower priority, making room for another buffer usable by a more urgent trafic, according to the routing QoS parameters.
QoS is a native part of IPv6 (where IPv4 only implements it in some non standardized semantics and where QoS parameters for the intended type of communication cannot be routed cleanly without using another helper protocol).
Generally, you won't need to specify QoS parameters for TCP, this is mostly used for real-time streaming, or for urgent UDP or ICMP signalization, because TCP is designed to be very tolerant about failures and transmission delays, and includes a recovery mechanism. However, streaming over TCP (notably over HTTP) is now become more frequent, and you may see some QoS parameters used as well for TCP with some real-time constraints (when the automatic recovery of TCP is not enough and does not offer a warranty for a minimum bandwidth, but just uses the default "best effort" routing strategy).
